Ole Gunnar Solskjaer admits Anthony Martial could miss Sunday's clash with Tottenham Hotspur.
The French forward has stepped up in Marcus Rashford's absence, scoring three goals in his last four Premier League appearances.
But Solskjaer might have to do without the 24-year-old in a match that could impact their chances of a top-four finish.
"Anthony hurt himself when he slid into the post [against Manchester City] so he's not ready for this game.
"Hopefully he can be ready for Sunday [against Tottenham] but I'm not sure. He's struggling a little bit."