Mathieu was hurt on a free kick after a Cardinals safety. After he was tackled on the play, Mathieu tried to run off the field and onto the Cardinals’ sideline, but he fell down before making it out of bounds.
Mathieu, who was attended to by the team’s medical staff, was able to sit up before being taken off the field on the cart.
The Cardinals have ruled out Mathieu for the rest of the game.
The 21-yard-old Mathieu has been a key contributor on the Cardinals’ defense this season, and he has shown the playmaking flair that marked his collegiate career at LSU.
The Cardinals hold a 23-3 lead late in the third quarter against the visiting Rams.