Ralf Rangnick is unsure why Marcus Rashford is struggling to make an impact after the Manchester United forward toiled in Monday’s narrow 1-0 FA Cup win over Aston Villa.

Liverpool great Steven Gerrard’s first match as a manager at Old Trafford was an entertaining occasion settled by Scott McTominay’s header in the eighth minute.

Villa had two second-half goals ruled out, the first after a lengthy video assistant referee review, but United had some opportunities to put the game to bed earlier.

Rashford was guilty of some poor decision-making in a couple of those moments and some met his substitution with sarcastic cheers.

Asked why the academy graduate was underperforming, interim manager Rangnick said: “Actually, I don’t know.

“I think he’s trying hard. In training he was doing well in the last couple of days, that’s why he was quite rightly in the starting XI.

“I think in the first half we found him quite often, but we also tried to get him into the box.

“In the second half that was not that often the case and that’s why at the end of the game I decided to make two changes with Anthony Elanga and Jesse Lingard.

“It was very important to progress into the next round. Yes, [confidence is important] especially for strikers – it’s important that they score goals on and off, that there are moments of success.

“Of course it would be good, for example, for Marcus if he could score a goal but as long as he’s trying, as long as he’s training well I don’t see that much of a problem.”

Rashford was far from the only below-par performer in a match Rangnick took some positives from as United got back to winning ways after last week’s 1-0 home loss to Wolves.

“We knew from the beginning that it will be a challenging game for us against a very flexible Villa side with their rotations that they’re doing during the game all the time between their full backs and their [number] eights,” he said.

“I think we saw quite a few pros today. I think we were better, we had a better structure.

“We also had good energy in the team, we moved the ball, in the first half especially, good within our team, with quite a few good diagonal balls.

“That was exactly what we intended to do against their rather central team and that was exactly the way how we created our first goal.

“But, as you said quite rightly, we’re still struggling in the centre of the pitch. That’s why Villa also had their moments where they could have scored.”

The helter-skelter encounter adds spice to Saturday evening’s rematch in the Premier League at Villa Park.

Marquee loan signing Philippe Coutinho could make his debut for Villa, whose manager Gerrard was left ruing what could have been on Monday.

“I thought the performance was good for large periods,” the Villa boss said.

“I thought we were dominating, we could have scored two or three goals tonight.

“I’ve got no complaints with what the players have given or the performance, but we go away frustrated because we’re knocked out of the FA Cup and we look to ourselves as to the reasons why.”

Villa scored two goals in the second half through Danny Ings and Ollie Watkins, but both were ruled out.

The second was a clear offside call but the first was more unclear to those inside Old Trafford, with Gerrard told it was because Jacob Ramsey impeded Edinson Cavani in the buildup.

“The officials took three-and-a-half minutes to settle that one,” Gerrard said. “They have looked at two or three things in it.

“When VAR is there and they make a decision, you have to accept it. There is nothing you can do to change it.

“The easy way out is to blame luck and the officials, we won’t do that.”