Last month, Calvin Johnson expressed his displeasure with how the Lions handled his retirement. Johnson didn't offer specifics, simply saying that he felt like he was mistreated on his way out. 

Now we might know why Johnson feels that way. 

According to the Detroit Free Press, Johnson paid the Lions at least $1 million when he retired in March of last year. Here's where I note that a certain former player named Barry Sanders experienced a similar problem when he retired.

It was always expected that Johnson would pay the Lions some amount due to his signing bonus from his 2012 contract, but it wasn't expected that the number would hit seven figures. When Johnson retired, the Lions said that his contract was "settled to the satisfaction of the parties." As the Free Press noted in its story, NFLPA records indicated that Johnson paid the Lions $320,000. But according to this report, Johnson paid more than triple that amount.

And so, Johnson's comments make a whole lot more sense now. A million bucks might make him feel this way.

"I don't even like to talk Lions too much just because the way our relationship ended," Johnson told the Free Press last month. "If they see me around here, we'll see. But hey, I don't know.

"I just didn't feel like I was treated the way I should have been treated on the way out. That's all. I mean, it's all good. I'm not tripping. I don't feel any kind of way, just hey, that's what they did. Hey, it is what it is."

In Johnson's nine-year career, he caught 731 passes for 11,619 yards and 83 touchdowns. From 2007-15, he ranked seventh in receptions, first in receiving yards, and first in touchdown catches. He was arguably the best receiver in the game and would've been a lock for the Hall of Fame if he didn't retire at age 30.

Not only did he give the Lions everything he had when he played for them, he reportedly gave them even more after he retired.