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.

With United lacking a cutting edge against their visitors, Rashford was introduced in the 64th minute and moments later, some confusion in the Wolves backline led to Juan Mata bursting clear and chipping over John Ruddy.

However, having been on the field for barely a quarter of an hour, a visibly discomforted Rashford headed straight for the tunnel, clutching his back for a few minutes after a challenge from behind from Matt Doherty.

Solskjaer admitted he took a risk in introducing a less than 100 per cent Rashford, who is now doubtful for the trip to runaway Premier League leaders Liverpool on Sunday afternoon.

"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," the United manager 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."

United, who will face either Watford or Tranmere in the fourth round, are without a number of first-team players because of injury, including midfield duo Paul Pogba and Scott McTominay.

But Solskjaer added: "It's football. I'd never, ever complain about all the injuries we've got, that's just part and parcel of it. Marcus has been available and fit all season so he can't complain."

Wolves were left frustrated by the video assistant referee as Pedro Neto's early strike was ruled out.

Fred's attempted clearance from a throw-in cannoned off Nemanja Matic and into the path of Jimenez, whose unwitting handball in a challenge with Harry Maguire meant Neto's calm finish counted for nothing.

The visiting fans chanted "it's not football any more" in frustration at the ruling, the second time across this tie Wolves have been left cursing the technology, with an identical infraction at Molineux denying Doherty a goal.

Wolves boss Nuno Espirito Santo said: "I didn't see the images yet but that's VAR. We are afraid to celebrate, we don't celebrate what's going on then Old Trafford celebrates a non-goal. It's VAR, something's wrong."

However, he took comfort from the overall performance, adding: "It was good I think we performed well in both halves. It was a good game.

"When you go out of a competition we are sad or frustrated but how we did it and how we played, it can move us forward. Let's try to sustain this level of performance and take our chances."