He was wrong. Eleven weeks later, Mathieu and three of his ex-teammates were arrested at his Baton Rouge apartment for marijuana possession.
Now, after undergoing drug treatment and seeking counseling, Mathieu is trying to restore his reputation and return to the game he loves.
"I know what it's like not to have football, I know what it's like not to be the center of attention, I know what it's like to be humiliated and I'm not going down that road again," Mathieu said Sunday at the NFL's annual scouting combine in Indianapolis.
It's certainly not the path Mathieu expected to take into the NFL.
A year ago, the hotshot cornerback with the catchy nickname "Honey Badger" was considered a Heisman Trophy front-runner.
Instead, he wound up in a two-week drug treatment program run by former NBA player John Lucas and tried to rebuild his image even as it continued to take hits.
When police searched Mathieu's apartment in October, they found a marijuana grinder, a digital scale and 10 bags of high-grade marijuana, seven of which were in another ex-LSU's teammate's book bag.
"That's when I decided to go to rehab," Mathieu said.
Since then, Mathieu insists he's cleaned things up - pointing to the fact he sought out counseling, got a sponsor and has refocused his efforts on making it in the NFL.
His height, he measured in at just under 5-foot-9, and his troubled history that are raising red flags among team decision-makers. A month ago, some analysts thought the laundry list of problems might leave Mathieu undrafted in April. Now, his stock is rising again and he's in Indianapolis like most of the other 300-plus draft hopefuls - trying to assuage doubts about themselves.
It's a tricky journey with a potential pitfall in every answer.
On Sunday, when Mathieu was asked about the last time he used an illegal substance of any kind, Mathieu blurted out Oct. 26, 2012 - the day after his arrest. Whether he was being honest, misunderstood the question or made a simple slip of the tongue didn't matter. If he does that again in the 15-minute team interviews, it could wind up costing him money.
How did Mathieu get himself into this mess?
"Half of it, I think, is that you actually start believing the hype, believing the clippings," he said, trying to explain what had happened over the last 12 months. "The other half, I think, is that you're young and you want to have some fun."
Adding a six-figure salary to the mix could complicate matters.
But Mathieu is far from alone in trying to find redemption in this draft. A handful of defensive back with character questions rolled through the media room at Sunday's combine. The list includes names such as:
• Bacarri Rambo, who failed two failed drug tests at Georgia;
• Sanders Commings, Rambo's former college teammate, who was suspended last season after being charged with domestic violence and faced his own battle with marijuana two years earlier;
• Greg Reid, who was booted off Florida State's team following last summer's arrest on marijuana possession charges;
• And Hawaii's Mike Edwards, who was kicked off Tennessee's team following a 2009 arrest for attempted armed robbery. Eventually, he pled guilty to reckless endangerment as part of a plea deal.
Each of the five, including Mathieu, expected questions about these issues.
Yet each used remarkably similar language to explain what happened, making it seem as if the answers were rehearsed, at best, or disingenuous, at worst.
"It's behind me. I'm moving on from that situation," Rambo said. "I'm a better person and I've learned from my mistake."
Mathieu, however, is could be the best known and arguably the most talented cornerback in the draft. He says he hopes to run the 40-yard dash in 4.4 seconds, fast enough to perhaps keep him in the upper echelon of cover cornerbacks in Indy.
But he hasn't played a game in 13 months, and by the time preseason games begin, the layoff will be 19 months.
Those who know Mathieu best believe he will excel in the pros.
"He'll make a big impact in the NFL, too," said ex-LSU teammate Tharold Simon. "A lot of people think he won't, but I know he will. He will be a key contributor in the NFL."
Others aren't so sure.
"I think he's a better football player than he is an athlete," NFL Network analyst Mike Mayock said. "He's short and probably speed deficient. He's probably a slot defender with return skills. I know he's going to come in here and say all the right things, but I think how he handles things with the teams is what really matters."
Mathieu is ready to put their angst to rest, too, and forget about his past.
Instead, he wants to spend the next two months focusing on what he has to do to get back in the game.
"I'm not focused on money right now. I just want to play football because I've played it my whole life for free," he said. "I know I made some mistakes. At the end of the day, I think I can overcome them."