Watch Now: Tiki and Tierney: Johnny Manziel to participate in developmental Spring League (2:53)

Johnny Manziel wants to play in the NFL again and he knows he's down to the last of a string of second chances. He revealed last month that he's finally sober and getting treated for a bipolar disorder. Last week, the 2014 Browns first-round pick threw at the University of San Diego's pro day and 13 NFL teams made a point to show up. 

And Manziel's comeback tour continues, according to FOX Sports' Bruce Feldman, who tweets that the former Texas A&M quarterback will throw at his alma mater's pro day on Tuesday to draft hopeful Christian Kirk and other Aggies receivers. And just like San Diego, NFL teams are expected to attend. 

At USD, Manziel went 36 of 40 in a light rain, though if history tells us anything it's that we shouldn't read too much into an offseason shorts-and-T-shirt workout.

That said, the issue has never been with Manziel's on-field ability but his struggles to avoid trouble off the field. He now says those days are behind him. In a conversation with Feldman earlier this month Manziel conceded that he has to prove that he's changed.

"When I first got in the league, did I have some leeway? Sure I did, but I have exhausted all leeway and all second chances," Manziel said. "This isn't the second chance. This is the 35th chance. This is the last of the last chances to show people that I've made a drastic change in my life, and it's for the better and I'm happy with where I'm at. ...

"[But] until I get into [an NFL] building and I'm able to show that, it's all just talk," he continued. "It's all just me saying that I'm different. Now, I know I am."

Whether Manziel is ever offered an NFL contract is yet to be determined but the fact that teams are showing up to watch him work out can only be taken as a good sign. ESPN's Eric Williams got confirmation that scouts for these 13 teams were in San Diego: Bears, Browns, Chargers, Giants, Chiefs, Jets, Patriots, Raiders, Titans, Lions, Jaguars, Panthers and Bucs.

And CBSSports.com's Jared Dubin broke down each of those teams' current quarterback situation in a previous post:

If Manziel stays on the straight and narrow and shows he can still play quarterback, it's reasonable to think this list will grow for one simple reason: quarterbacks are hard to find.