Manchester United are waiting to learn the severity of injuries suffered by Edwin van der Sar and Louis Saha.
Van der Sar was forced off at half-time during Saturday's FA Cup defeat to Portsmouth after picking up a groin injury.
United are unsure how serious the Dutch goalkeeper's problem is, but he is a worry for next weekend's game with Derby County.
If Van der Sar fails to recover in time for the trip to Pride Park, it could see Ben Foster make his debut for United.
Tomasz Kuszczak, who replaced Van der Sar against Portsmouth, will be serving a three-match suspension after his red card for bringing down Milan Baros.
That will leave Foster, who has only just recovered from a long-term knee injury, as United's sole senior keeper for the match against the Premier League's bottom club.
The fitness of Saha is also a concern for United boss Sir Alex Ferguson after the French striker was withdrawn from the Pompey defeat.
Saha had been pencilled in to start the quarter-final tie, but aggravated a knee injury in the warm-up.