Romelu Lukaku suffered an ankle injury against Arsenal a fortnight ago
The Belgium international suffered an ankle injury against Arsenal a fortnight ago and is battling to be fit to face his old club.
Mourinho had originally said the striker could be fit enough to make the bench at Wembley.
But the manager has now hinted he may not play at all as the club continue to check on his injury.
Mourinho did have some good news, though, confirming Anthony Martial is available after a knee injury suffered in training.
The Red Devils boss said on Friday: “Anthony Martial is fit but with Lukaku we will have to wait.
“We have to wait until the last minute, I won’t lie to you.”