Rams wide receiver Mark Clayton suffered a season-ending knee injury Sunday, according to the St. Louis Post-Dispatch.
Clayton left against the Lions in the first quarter and didn't return as the Rams lost 44-6.
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.
The Associated Press contributed to this report.