Westbrook remained on the ground for several minutes before he was helped up and led off the field directly to the locker room. The Eagles said he was not expected to return.
Westbrook had three carries for 13 yards at the time he was hurt.
In the second quarter, Redskins tight end Chris Cooley left the game with a right ankle injury. He was the fourth Washington player to have an injury announced, following cornerback Byron Westbrook (knee), linebacker H.B. Blades (knee) and defensive tackle Cornelius Griffin (sprained elbow).