The Rams tweeted the news Wednesday, but didn't provide details. They also placed cornerback Jerome Murphy on injured reserve, put cornerback Marquis Johnson on the physically unable to perform list and signed defensive tackle Marlon Favorite.
Clayton went down with a right knee injury in a game against Detroit and had season-ending surgery on his torn patella tendon. He had 23 catches for 306 yards and two touchdowns before getting hurt.
Acquired from Baltimore just before the start of the 2010-11 season, Clayton has 257 career catches for 3,422 yards and 14 touchdowns. He played his first five NFL seasons with the Ravens.