Steelers safety Troy Polamalu is unlikely to play Sunday against the Chiefs, but his knee injury isn't considered serious. Polamalu strained the posterior cruciate ligament in his left knee on Sunday against Bengals. He sprained the medial collateral ligament in that same knee Sept. 10. "More encouraged than I think we initially anticipated," coach Mike Tomlin said Tuesday. "There is no setback in regards to his MCL. We're going to take it day by day. (The injury) doesn't appear as significant as the MCL he sustained earlier in the season."