He has overcome the odds of a seventh-round draft pick and not only made an NFL roster, but become the No. 2 quarterback for an NFL team.
Although the rookie from LSU is entering only his fifth week of NFL duty during the regular season, he may encounter his biggest obstacle yet when the Green Bay Packers host the Atlanta Falcons on Sunday.
Because Aaron Rodgers' sprained throwing shoulder was a bother Friday, it seems more and more possible the former Tiger will be under center Sunday.
Ask anybody, and they have an opinion on what should happen. It boils down to how Rodgers feels on Sunday morning. If the shoulder remains a pain, Flynn enters his biggest moment of his career.
Fortunately for the Packers, they are not playing the Baltimore Ravens, Pittsburgh Steelers or Philadelphia Eagles, the top-ranked defenses in the NFL. Flynn gets the Falcons, a unit that is ranked 20th, and he's home.
McCarthy said he worked a little more with Flynn and No. 3 quarterback Brian Brohm this week, as Rodgers' practice time has been virtually nil. Like any coach, he has confidence in his backup.
He really should, otherwise, why is he No. 2?
"I think you have to admire Matt Flynn's disposition, the way he approaches football," McCarthy said. "Nothing rattles him. He practices the same every day, as far as his demeanor and so forth."
Many doubt Flynn's ability to play well after watching him last week, as he looked overmatched in a couple of series at Tampa Bay. Consider how few snaps he gets with the first unit during the week when Rodgers is healthy, and it's hard to look like a seasoned veteran, especially against that Buccaneers defense.
But give him a week to prepare, get comfortable with the idea of starting and actually working with Donald Driver, Greg Jennings and Donald Lee. He hasn't thrown too many passes in their direction, so the timing can't be perfect.
No question, if Flynn starts, the types of plays called will be different than if Rodgers was playing. It'll be simplified, and McCarthy will do everything in his power to not put Flynn in a position to have to win the game. He'll try to make him the ultimate game manager.
The one thing going for Flynn is he's played on the big stage before — last year's BCS national championship game, in which LSU whipped Ohio State in January. That's the best preparation a rookie can have as he enters his first NFL start. It's one of the reasons McCarthy isn't sweating — publicly, at least — about Flynn starting Sunday.
"I don't worry about the game as far as the environment," McCarthy said. "He's played in big games. Matt's won a national championship, which speaks for itself.
"It's just, I say it all the time, him and Brian, they need reps. They need those reps playing at full speed and seeing those different looks the defense is going to give you. He'll be ready to go."
As ready as he can be.
Flynn's possible debut as a starter shouldn't be overanalyzed, as I'm sure it will be. If he struggles, people will say he can't make it in the NFL. I remember the last couple years how many people said Rodgers can't cut it in the NFL after making brief appearances in games, especially that Monday night debacle at Baltimore, where the Ravens' defense overwhelmed him.
I never said Rodgers was a bust. I reserved that call for when and if he failed as a starter. So far, no need to call him anything but a success.
Also, one game doesn't define how good a player is. If he lights up the Falcons' defense, he isn't the second coming of Brett Favre.
Flynn's possible start Sunday will be a glimpse of what he can do early in his career. It gives us no indication of how good he can be two years from now. But if his college success is any barometer, who knows, the Packers may have a seventh-round steal on their hands.
Doug Ritchay is a frequent contributor to PackerReport.com. He has covered the Packers since 1993. E-mail him at firstname.lastname@example.org.