TEMPE, Ariz. --
The news on
was even worse than expected, as an MRI on Monday morning revealed that Mathieu has a torn ACL and LCL (
lateral collateral ligament
). Both injuries were sustained while Mathieu was returning a kick in the third quarter of Sunday's game against the St. Louis .
Clearly, Mathieu is out for the rest of the season, but coach Bruce Arians said Monday that the recovery for this surgery will be even longer than ACL surgery with the LCL factored in. The normal recovery period following ACL surgery is six to nine months.
"He was crying," Arians said when asked how Mathieu handled the news. "When these guys get hurt for the first time, it's devastating. To take away the thing he loves most and worked hard for is devastating."
When asked if Mathieu might be ready for training camp at the end of July (seven and a half months from now), Arians quickly dismissed that possibility, saying, "I would doubt that."
Much will depend on how fast Mathieu's body heals and the rehab process, but it is fair to say that Mathieu's availability for the 2014 season opener is in doubt.
"This will be a long one," Arians said. "I won't attempt to say how long because it’s (based on) individual guys."
A source familiar with the procedure said Mathieu won't likely be able to put any weight on the knee for anywhere from one to two months after surgery, depending on the healing process, and Mathieu could wait up to two weeks before having surgery to allow fluid to drain from the knee.
With him out of the lineup, the Cards will turn back to
, who was the starter when the season began.
"That's what this league -- it's a league of great players, and when somebody goes down, an opportunity presents itself," Johnson said. "I'm ready. There's not going to be a letdown on the defensive side.
"I was able to accept my role when it grew smaller. Now it's going to grow, and I'll still have to do what I need to do."
Aside from Johnson's move into the lineup, Arians said Mathieu's position(s) will be manned by committee. Arians noted that cornerback
filled in well on Sunday, but
are also possibilities to replace the injured free safety and nickel corner.
"But now you have to substitute to get what we had before with a non-substitution situation," Arians said.
Mathieu played in 13 games and took over for Johnson as the starter in Week 4 in Tampa Bay after Johnson lost his fingertip on a freak play against New Orleans in Week 3. He had 63 tackles -- second best on the team -- along with two interceptions and a forced fumble, and he was named NFC Rookie of the Month in October.
How much will the Cards miss him? Of 884 defensive snaps through 13 games, Mathieu played in 779 (88 percent), and in the five straight games before Sunday, he had played at least 99 percent of the snaps along with 126 snaps on special teams, leading to talk of him winning the NFL Defensive Rookie of the Year award.
"To me, he's a lock," Arians said. "No one else has played as much as he's played, and all the positions he's played."
Although he clearly won't be able to play in the game now, Mathieu was sixth among free safeties in the latest Pro Bowl voting with 42,359 votes. And although his season is now over, it was a remarkable year for the rookie, who missed the entire 2012 football season after being kicked off LSU's team.
The Cards took a gamble drafting Mathieu in the third round, reasoning that with good friend
in town and Mathieu eager to atone for past mistakes, he would be able to toe the line and the Cards could have a first-round talent. Clearly, that gamble paid off.
"Very seldom do you see guys come in and be a leader like he has," Arians said. "His personality is infectious with the guys because he loves football. He'll stay out there and practice all day and go as hard as he can. Those are guys you miss. He's got a bright, bright future."
Mathieu is the fourth 2013 draft pick the Cardinals have lost. Top pick
broke a leg in the preseason, sixth-round pick
, a receiver from Texas A&M, retired before training camp due to multiple concussions, and fourth-round pick Alex Okafor suffered a torn triceps before the team's game in Tampa on Sept. 29.