Marcus Rashford missed training on Friday morning after an illness forced him to postpone his flight back to Manchester, having enjoyed a midweek night out at the Thompsons Garage club in Belfast.
Footage on social media showed Rashford entering the Belfast night club on Wednesday night.
Sources close to Rashford say he was out for dinner and had to postpone his flight home after being taken ill.
Erik ten Hag revealed that the England international's absence was down to illness during his press conference ahead of their FA Cup fourth-round clash against Newport County on Sunday.
'This morning, Rashford was ill, and Evans was ill,' the United boss said. 'So we have to see how they recover, but we have, for the rest, players returning, like Martinez, like Shaw, like Maguire, like Casemiro, which is a good thing.'
Marcus Rashford had been seen entering Belfast night club Thompsons Garage on Wednesday
The Man United forward did not attend training on Friday morning after an illness had forced him to miss his flight back to Manchester
Thompsons Garage is located in the city centre of Belfast and is open seven nights a week
Mail Sport have reached out to Manchester United and Marcus Rashford's representatives for comment.
Rashford was also seen visiting the training ground of NIFL Premiership side Larne during his trip, where his former United teammate Roshaun Williams now plays.
Mail Sport understands that Rashford had gone out on Wednesday before having had a day-off on Thursday.
It comes after he risked the wrath of his manager after he went out clubbing following United's disappointing loss to Manchester City back in October.
The Red Devils suffered a 3-0 defeat by Pep Guardiola's side, with Rashford heading to the high-end Manchester nightspot Chinawhite to celebrate his 26th birthday.
The party had finished at 3.30am but it is not clear if Rashford had stayed until then.
Ten Hag addressed the matter back in Octobeer, saying: ‘I spoke with him about it. It’s unacceptable. He apologised and that is it. For us it’s an internal matter.’
The Dutchman added: ‘He [Rashford] is very motivated to put things right. He’s totally with us.
‘He has made a mistake but that doesn’t say he’s not fitting in. I see him every day in training, what he’s doing, I know.’
Ten Hag revealed that the forward could be in danger of missing their FA Cup clash agaist Newport County on Sunday due to the illness
Rashford had previously risked the wrath of Ten Hag after he went on a night out following Man United's 3-0 defeat to Man City back in October
After scoring 30 goals for United last season, Rashford has endured a difficult campaign so far scoring four times in all competitions
On the pitch, the 26-year-old has endured a frustrating campaign, netting just four times in all competitions, compared to his 30-goal mark last term.
Despite that, he has scored in two of his last three appearances for the Red Devils, including their recent 2-2 draw against Tottenham.
Erik ten Hag's side are currently preparing for their trip to Newport on Sunday which could prove tricky in the uncomfortable surroundings of Rodney Parade.
After finishing bottom of their Champions League group and getting eliminated from the Carabao Cup, the FA Cup provides the only genuine opportunity to claim silverware this season.