Manchester United midfielder is facing surgery and two months on the sidelines after suffering knee ligament damage in his cameo against Tottenham.
The big-haired Belgian came off the bench during Wednesday’s 2-0 defeat at Wembley, but he lasted just seven minutes and 29 seconds before being subbed off again.
Fellaini was brought on in the 63rd minute, but picked up the problem moments later when he attempted to get the ball from Spurs star Christian Eriksen.
Fellaini will have scans on the injury at the club’s Carrington training ground on Thursday to determine the extent of the injury.