PHOENIX -- The hours of torturous rehab, including squats with 245 pounds on two surgically repaired knees -- one just fixed in early January -- could break even the toughest man.

Hell, it hurt just to watch. My own knees felt the pain as Tyrann Mathieu went through his four-hour rehab on this Wednesday in late March. It would be easy to understand if Mathieu had any hesitation to continue, the reluctance to drive himself losing out to the desire to stay home in bed with a good movie or take his kids out for ice cream.

Yet Mathieu, the Arizona Cardinals' do-everything defensive back, went through his workout like it was a warm-up for a game. With his own private music playing in his ears, even as the loudspeakers above blared club-decibel songs to the other NFL players rehabbing and working out at the Fischer Institute here in Phoenix, Mathieu hardly resembled the player whose on-field ferocity earned him the nickname of the Honey Badger in college at LSU. Calm seemed to be the approach.

It was a businesslike, structured workout that seemed at times to put Mathieu into his own little world, a zone where focus is key with little time for distractions. With a big brace protecting his recently repaired right knee, Mathieu took the 245 pounds of weights off the rack, put it on his shoulders and then went up and down with it eight times. It was one group of reps on one of several exercises this day, but the determination came through loud and clear on this painful-to-watch set.

"He gets after it," said Brett Fischer, the owner/operator of the facility who is rehabbing Mathieu and seems like a proud dad when he leads him through it. "I love working with him. He's so intense."

Mathieu heard Fischer's remarks, and looked up during a break.

"Just work," he said. "Just work."

That's his motto every single day.

Just work.

Fischer then pointed to his notepad where he jots down Mathieu's progress each day. He also had written down the date of his surgery: January 5.

"Just so I remind myself that he needs to slow down sometimes," Fischer said. "Two words sum him up here: Passionate and hungry."

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Mathieu might be coming back from a knee injury, his second, and that's a daunting task for anybody. It's nothing compared to his biggest comeback, which is also one of the biggest in sports history: Mathieu rallied to beat himself.

Knee rehab? Big deal.

Life rehab? The greatest win of all.

As Mathieu joined some players later here during his workout, lifting his legs over some hurdles, the picture was a perfect image for his life. Going over one hurdle, there always seems to be another right behind it. This is a kid who was raised by an uncle and an aunt because his father was in the prison system for murder and his mother abandoned him. This is a kid who grew up around trouble, smoked pot for most of his life and ended up in a jail cell in Louisiana, even though he was a football star with a catchy nickname -- his own bad choices putting him there.

Then after getting a second chance with the Cardinals, who took him in the third round in the 2013 draft, Mathieu tore his left ACL in December of his rookie season. Then on his way to his first Pro Bowl last season, he tore up the other knee.

How much more can one guy take?

"These are the kinds of situations that build character and build a man," Mathieu said after his workout. "As long as I can put that in my mind and keep those things in front of me, I will be all right in the long run."

Tyrann Mathieu says he's moved on from making excuses for himself. (USATSI)

Much of who he is today was shaped by who he used to be. On his way to football stardom, becoming a college legend of sorts, his nickname becoming well known to many, he ended up kicked out of school and wound up spending 12 hours in a jail cell after being arrested for possession of marijuana in October of 2012.

It was in that cell that day, a place where he once said he contemplated suicide, that he was also taught a valuable lesson by some of the inmates, many who were shocked and angered to see one of their football heroes in a hellish place with them.

"When I walked into jail, all the inmates were disappointed at me," Mathieu said. "It was one of those reality checks for me. I had to sit in a cell by myself. If they had put me in cell with them, they would probably try and beat me up. It was a reality check for me. They loved me. But it was a simple fact the apple doesn't fall from the tree. I was one of those that was fortunate enough to make it. They felt everything I did was for them, and it was almost a spit in their face.

"Sitting in the cell, I can feel their energy. They're yelling across the room. If the guards would have opened that gate, they would have got to me. It was one of those situations where I said this is not just about me. I affect so many people. Criminals. Successful people, educated people, misfits, guys who don't have a father. I represent a lot of people. For me to take that for granted, that was the day I realized (he had to change). My birth father is in prison. My birth mother basically abandoned me. I was supposed to be raised by my grandparents, but my grandfather died. I was adopted by my uncle and aunt -- who are now basically my parents. For me, I always felt I had an excuse to smoke pot and do all sorts of things that knuckleheads do. I woke up one morning after I went to jail and said I don't want to be that person anymore. I am tired of making excuses for myself. I am tired of letting people down. Most importantly, I am tired of disrespecting myself."

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Mathieu left Louisiana and came to Arizona to live with former LSU teammate and current Cardinals teammate Patrick Peterson. The Cardinals drafted him in the third round later that year and the two now play in the same secondary again, which is one of the league's best.

He is drug-tested regularly and has stayed clear of trouble since coming to the Cardinals. He has become a bit of a recluse of sorts. Cardinals coach Bruce Arians says it's nearly impossible to get Mathieu away from the home he shares with his wife and two sons, even for a charity golf tournament. Mathieu did attend a recent Peterson event to support his good friend. But those who were there say he kept a low profile away from most of the action.

That's who he's become.

That's who he needs to be. When I asked him how the other Honey Badger would have handled a second knee surgery and the trials and tribulations that come with it, he surprisingly had a matter of fact reply.

"I probably would have smoked so much marijuana I would forget about it all," he said. "Nowadays, that's not my escape anymore. I want to handle things head on."

The past, he says, has helped mold him into who he's become. On a recent trip back to Louisiana for the funeral of his grandmother, he was reminded of how fortunate he was to get out of there. I asked him where he'd be if he didn't leave? Would he be dead or in jail?

"My best friend that I grew up with is dead," he said. "He was murdered and most of my uncles and cousins are in and out of jail. That apple doesn't fall far from the tree. I would probably be either or."

Mathieu was a Heisman finalist at LSU before being kicked out of the program. (USATSI)

That's why he works so hard to be a great teammate, player, husband and father to his two boys. This is his second chance at life. He's not about to let two knee injuries, even severe ones, ruin that.

To watch him attack his rehab is impressive, and you can feel the desire to provide for his kids as he goes through each painful part of it. He appears to ease through it, but he admits there have been moments when he's gotten on Fischer too much, the pain, the agony and the constant drive to be better taking a toll on his mental approach.

Yet he's there every day for long, intense sessions. There was no self-pity after the second knee injury last November in that nationally televised Sunday night game against Philadelphia. That's because there was too much work to do to get back to what he says was playing the best football of any secondary player in the league.

"I've been depressed before," he said. "I've played that card already. Having self-pity. Trying to find every kind of excuse in the world of why I shouldn't continue to go forward. This time, I didn't use that excuse. I hit the ground running. I knew what was expected of me. I knew what direction I wanted to go in. I knew what kind of player I wanted to be. This is my safe haven. I am so relaxed here. The more I stay here, the more I feel like my goals are going to come to fruition."

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Before this knee injury, Mathieu was starring as the new-wave hybrid player in the Cardinals secondary. With offenses now so spread out, Mathieu is a revolutionary of sorts, a player who can cover the slot receiver, play safety, blitz or carry the tight end down the seam.

He is a bit of a trendsetter as teams look for players of his skill-set. Good luck with that.

"A lot of people get stuck as a cornerback or a safety," Mathieu said. "They want to be defined by one particular position. For me, 'Coach, please don't define me as one particular position. I am smart enough play every position on the field and I am tough enough to play any position on the field."

Mathieu prides himself in being able to take on any assignment, from TEs to wide receivers. (USATSI)

OK, so maybe not defensive line. But he has lined up in almost every spot on the back end. That's talent. It's also value, which is why his upcoming contract negotiation will be interesting to watch.

He's entering the final year of his rookie contract, and without the knee injury last year he probably already has put pen to new contract. Instead the knee injury has slowed him getting what can be described as generational money on a new deal, the kind he can hand down to his kids and grandkids.

Mathieu said he would love to stay in Arizona, but he also understands that the negotiation might be tricky with him coming off two knee surgeries. The Cardinals love him. They always say so, especially Arians. The Valley of the Sun has adopted him as a favorite son, and he's a great teammate. So you would expect something to get done.

"They have concerns, which is understandable," Mathieu said. "I've had two knee surgeries. At the same time, they know who I am as a teammate, as a football player, what I mean to the community and what I can do on the football field. The easiest thing is to pay me as a safety. But if Pat's guy goes down, I have to check Pat's guy. For me, it's about me being compensated for everything I do.

"As I walked off the field in Philadelphia, it was like, 'Damn, my whole purpose is to take care of my family.' I want my sons to have the best life. I don't want them to do the things that I did. It was gut-wrenching because it wasn't just about football. It was about me providing my family a life they've never seen before. But also being out there with my teammates. It was different without me."

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Mathieu recently changed his diet to help his rehab and improvement on the field, like Peterson did last year for health reasons -- which helped him have his best season. Mathieu has cut out sugars and gone to a mostly organic and gluten-free diet. The result was that he dropped down to 175 pounds recently. This former candy addict -- anything and everything was consumed, he says -- feels better than ever. He is currently in the process of adding weight and would like to play at 190 in 2016.

Mathieu says he wants to be compensated for his all-around game. (USATSI)

"I can't tell you how much better I feel every day," Mathieu said. "I just had surgery two months ago and I am able to do five- and six-hour workouts. I don't run home and try and take a nap. I run home and do some sit-ups. Try to get yoga. I am not tired. I am in such a great place. I am going to be better than I was. In order for me to be who I want to be I have to sacrifice something. I always hear J.J. Watt say that. And he's probably the best player in the game right now -- defensively. He always talks about sacrifice, sacrifice, sacrifice. I take heed to that."

Watt, a notorious worker, would be proud if he could watch Mathieu rehab. From running on a treadmill suspended by a harness, to squatting and doing a variety of other things, he attacks it with vigor. The next big step, according to Fischer, will be lateral cutting. Then it's defensive back drills. Then it's covering receivers, which will likely happen in training camp.

The target date for Mathieu's return is opening day of the regular season. He wants to be full go for that game.

Will he make it? "Absolutely, without a doubt," he said.

After the comebacks he's already been through, especially winning in the game of life after falling behind by two scores, who the heck will doubt him?