Cardinals rookie Tyrann Mathieu tore ACL in Sunday's win

Tyrann Mathieu was carted off the field on Sunday with a torn ACL. (Christian Petersen/Getty Images)

Cardinals rookie safety Tyrann Mathieu tore his ACL in Sunday's 30-10 win over the St. Louis Rams, a development that serves as a big blow to the league's sixth-ranked defense.

Head coach Bruce Arians said after the game that it "appears" Mathieu suffered a torn ACL, and an MRI on Monday confirmed that, according to ESPN's Adam Schefter.

Mathieu has emerged as a key cog in the Cardinals' highly ranked defense, one year after being kicked off LSU's football team for failing multiple drug tests. He had 67 tackles along with a sack and two interceptions this season.

At 8-5, the Cardinals head into the final three weeks of the season one game behind NFC West rival San Francisco for the second wild-card spot.

After the injury, Mathieu tweeted this:

I appreciate everyone prayers. We go through things in life to test our faith & strength..
— Tyrann Mathieu (@Mathieu_Era) December 9, 2013

Cardinals DB Tyrann Mathieu did tear his ACL, a league source confirmed, as Arizona feared.
— Adam Schefter (@AdamSchefter) December 9, 2013