Safety Rashad Johnson, picking an interception in Sunday's 30-10 win over St. Louis, is starting again after Tyrann Mathieu suffered a season-ending knee injury.

Tyrann Mathieu was at the Cardinals' facility for a short time Monday morning, getting some early treatment on a left knee that needs much more than that.

The initial Sunday diagnosis on the rookie safety's injury was confirmed and then some a little while before, as the Cardinals learned Mathieu had torn his anterior cruciate ligament and the lateral collateral ligament. The injury sounds ugly and it is, with surgery in about eight to 10 days and a rehab timeframe that had coach Bruce Arians doubting Mathieu can return for

training camp 2014.

"You feel bad for the person," cornerback Jerraud Powers said. "You know the long road it takes to get back and that's what you picture, not so much as how it affects the team and 'What are we going to do next.' It's about him personally.

"You feel for him. Mentally it will be a challenge. But if anyone can do it, Tyrann can. He's been through more than anyone else in this locker room the last three years or so. This is minor compared to what he’s already dealt with."

Indeed, Mathieu already was using social media for positive thoughts, putting on Instagram the belief "For every minor setback comes a major comeback."

If there was any concern how Mathieu, with his past personal issues, would handle the dead of the offseason, it no longer will be a factor. Now, Mathieu figures to spend much of his time at the team facility undergoing rehab.

Arians emphasized he wasn't worried how Mathieu will handle the injury. The LCL injury lengthens the rehab process, but Arians wouldn't put an official time frame on it because each individual is different.

The Cardinals certainly don't have him for the last three games of this season – and any potential postseason games – so adjustments will have to be made. Rashad Johnson had been starting at free safety early in the season and he will return to that role.

"I've always been a guy that kind of never looked at it as starting, not starting," Johnson said. "My mindset was, I step

between the lines and I am going to do what I know because I know I am going to do my job, whether I was starting or just in the nickel package. Being a starter is really just a name that you get, but it doesn't mean anything to me."

Veteran Antoine Cason has filled in on the outside, while veteran Javier Arenas has not only played a little safety but also nickel cornerback. Arians also mentioned Bryan McCann. But Mathieu's versatility has been priceless. His ability to play safety, cornerback and the nickel has allowed him on the field for 90 percent of the team's 866 defensive snaps prior to his injury, and all but three defensive snaps in the last six games.

"He meant a lot to us with his flexibility and his positions," Arians said. "It will take two guys to take his place."

Johnson, who made an interception late in Sunday's game, said the Cards will be hurt to lose a dynamic playmaker. And he agreed with Arians that substitutions will be more important because multiple players will be necessary to replace Mathieu.

But Powers was confident that with a secondary full of veterans, the Cardinals' defense will be able to transition to new pieces.

"From a fan's point of view, all they see is Sunday," Powers said. "They don't see all the work you put in. You can't fault them for that … (but) they just need to know guys have been putting in the work all season. So whoever the next man is up, expect the same type of production and he needs that same type of support like you'd give to Tyrann."

EXTRA POINTS

Arians said that how he treats quarterback Carson Palmer and his sore right elbow in practice this week "is a wait-and-see thing." Palmer did not throw a pass at all in practice last week although he played and played well against the Rams. "I'd like to see him get a little more (practice) than last week," Arians said. …

Arians acknowledged wide receiver Michael Floyd is beaten up a bit. "The season has taken its toll on him," Arians said of Floyd's shoulder and ankle issues, among others. "As long as the ball is in the air toward him, he'll be fine."