Levi Colwill was forced to pull-out of Chelsea's starting XI for their FA Cup tie against Aston Villa after picking up an injury in the warm-up, with youngster Alfie Gilchrist called up to replace him.
Colwill was picked for the Fourth Round tie by Mauricio Pochettino, but went down the tunnel after warming up for about a minute.
The defender's knee was already heavily bandaged and his absence is a major blow for the Blues.
Another Blues academy product, Max Merrick, took a spot on the bench following Gilchrist's promotion to the starting XI.