On Thursday, his latest hurdle was learning how to run with his new knee brace.
"It's bulky," he said. "When I'm running, I kinda got to pick my leg up kinda."
While Mathieu was explaining how the brace impacts his stride, he was giving a group of reporters a demonstration, bringing his knee high to his chest, over exaggerating a bit in the process. The brace, however, isn't restricting his football moves, he said. It's just taking him time to get used to.
On Friday, Mathieu practiced with the scout team against the first-team offense for a second straight day. He nearly picked off quarterback Carson Palmer on a pass to John Carlson but Mathieu looked to be a second too late and backed off at the last moment.
Mathieu's debut may not come Sunday night against Cincinnati. Cardinals coach Bruce Arians said he was going to evaluate Friday's practice and make a decision Saturday.
"I wasn't trying to hit them," Mathieu said with a slight smile. "But I put a little weight on."
Mathieu said he gained about 12 pounds of upper-body muscle, which, he said, led to the hits. But as soon as he dropped Ellington, Mathieu was scared for a second.
"Actually, I thought he was going to throw me out of practice," Mathieu said of Arians. "He doesn't usually let people hit Andre.
"Luckily, I was able to stay in practice."