Knight suffered the injury while diving on a third-and-goal play late in the first half. X-rays were negative.
Bell, who threw a 7-yard touchdown pass to Jalen Saunders with 19 seconds remaining to lift the Sooners past their rival, finished 10-of-16 passing for 140 yards.
Before the injury, Knight had completed 3 of 7 passes for 28 yards and rushed for 47. He led the Sooners into field goal range late in the second half, allowing Oklahoma to tie the score at 10.