Steelers coach Mike Tomlin said Polamalu was undergoing an MRI exam. Polamalu missed four games earlier with a torn medial collateral ligament in his left knee before returning Oct. 18 against Cleveland.
Polamalu apparently was injured tackling Cedric Benson during Cincinnati's opening possession, which ended with Shayne Graham's missed 51-yard field goal attempt. Polamalu could be seen flexing his knee after coming off the field, and he left for the locker room shortly after that.
Polamalu, a five-time Pro Bowl player and one of the NFL's top defensive players, was escorted to the locker room by team physician James Bradley, rather than a team trainer -- as might be the case with a less-serious problem.