Rookie strong safety T.J. McDonald was fitted for an air cast and carted off the field after getting his leg caught in traffic in the third quarter.
Two sources informed of the injury told NFL Media Insider Ian Rapoport that McDonald suffered a leg fracture on the play.
Veteran nickelback Cortland Finnegan also exited with a thigh injury. Having lost a step from last season, the 29-year-old has been among the least effective cornerbacks in the league through four games.
UPDATE: The Rams placed McDonald on their injured reserve designated to return list Friday.