Ole Gunnar Solskjaer admitted his decision to bring on Marcus Rashford "backfired" after the Manchester United forward sustained a back injury in the 1-0 FA Cup third round replay win over Wolves.
The United striker landed awkwardly after tangling with Wolves full-back Matt Doherty and was replaced by Jesse Lingard in the 80th minute of the game, having come on as a sub himself in the 64th minute.
United went on to set up a fourth-round tie against the winner of the replay between Watford and Tranmere Rovers.
Rashford was the first United player to come on as a substitute before then being substituted himself in the same FA Cup match since Alan Smith against Liverpool in February 2006.
"I didn't want to play him. I think he got a knock, a knee or something, in his back, but he's been struggling for a little while," Solskjaer said of Rashford, who has scored 19 times for United this season.
"That's why we've kept him away (from starting against Wolves), but we needed the win. He was involved in the goal so that was a positive but it backfired.
"He's a quick healer and he'll play through some pain, definitely, if he's capable and it's not a bad, bad injury, but we've seen that he's struggled lately.
"But that's been more when he's been tired. He wasn't on long enough to be tired so it might be something that just happened there and then.
"He's been absolutely top this season so we'll do anything and everything we can to get him fit for Sunday. If he's not then we'll play without him."
Rashford expressed his frustration at having to be substituted, writing on Twitter: "Never want to feel like I've let my team-mates, the club and most importantly the fans down so did my very best to carry on tonight and was gutted to come off.
"Top work from the lads to get into the next round."