The Ravens drafted Mosley with the No. 17 pick in 2014.
Ravens linebacker C.J. Mosley suffered a bone bruise after a play in the first quarter and didn't return to Thursday's 34–23 loss to the Bengals, the team announced.
He was carted to the locker room shortly after, and was being evaluated for a knee injury.
Mosley has been a key piece of Baltimore's defense since the team drafted him out of Alabama with the No. 17 pick in 2014.
After Mosley exited the game, the Bengals went on to score the game's first touchdown when Andy Dalton connected with A.J. Green on a four-yard pass.
Mosley, a three-time Pro Bowler, has only missed two games in his entire career, and both came during the 2016 season. He is in the final year of his contract and Ian Rapoport of NFL.com reports the Ravens and Mosley have not been close on agreeing to an extension.
After the game, coach John Harbaugh said Mosley had an MRI and it revealed no ligament damage.
The Ravens' next game is at home vs. the Broncos on Sept. 23, and Harbaugh said he has "no idea" if Mosley will be ready to play.