But Cardinals general manager Steve Keim won't wager his paycheck that Mathieu, who tore his ACL and LCL in Week 13, isn't suiting up for Week 1 against the San Diego Chargers on "Monday Night Football."
"I really think it is still too early to tell," Keim said on Schein on Sports on Sirius XM NFL Radio on Thursday. "But when people have asked me before if he's going to be ready for the first game, I would tell you this: 'If I was going to Vegas, I wouldn't bet against him.' "
Mathieu is still on the physically unable to perform list, although Keim said Mathieu "yelled" at the GM Wednesday to take him off the list. Being on PUP limits what Mathieu can do during practice. He's spent the first week of training camp rehabbing his knee and jogging but mostly watching practice from the sideline.
Keim said Mathieu's rehab has advanced recently.
"I actually watched him work out a little bit yesterday and he looks phenomenal," Keim said. "He's gotten into the point of his rehab where he's doing [defensive back] drills, change of direction. He looks quick. He looks explosive.
"He's foaming at the mouth, as well. That's just the way he is. He wants to play but we got to be smart about it. We got to listen to our doctors and medical staff. We're going to be smart about it."