"It doesn't look good," Rams coach Steve Spagnuolo said. "We'll know more tomorrow, but they said it had something to do with the patella. We're not optimistic."
Clayton fell to the ground while running a deep pass pattern along the left sideline and stayed down until he was carted off the field. He caught a pass for 6 yards earlier in the game.
Clayton entered the game tied for fourth in the NFC with 22 receptions. His injury put more pressure on Danny Amendola as rookie quarterback Sam Bradford's top remaining target. Amendola caught 12 passes on the day for 95 yards.