Updated at 23.07

MANCHESTER UNITED manager Erik ten Hag says it was “unacceptable” of Marcus Rashford to go a nightclub party after last weekend’s embarrassing derby defeat to Manchester City.

The homegrown talent has managed just one goal for the misfiring Red Devils during a poor start to the season on both an individual and collective level.

Rashford has looked a far cry from the player that plundered 30 goals for United last term and his off-field decision-making came into question after last Sunday’s 3-0 defeat to City.

Reports emerged the following day that the England international, who turned 26 on Tuesday, had gone to the Chinawhite nightclub for a pre-arranged birthday party hours after the Old Trafford loss.

“Yes, I am aware of it,” manager Ten Hag said of Rashford’s post-derby night out.

“I spoke with him about it. It’s unacceptable, I told him, he apologised and that’s it. For the rest it’s an internal matter.”

Ten Hag repeated it was an “internal matter” when asked if Rashford had been fined for an incident that he says will not impact his availability for Saturday’s crunch Premier League trip to Fulham.

The United boss also clarified that his place among the substitutes in Wednesday’s 3-0 Carabao Cup exit to Newcastle was due to rotation rather than punishment.

Rashford was dropped to the bench at Wolves last season for timekeeping, but Ten Hag rejected the notion that the academy graduate is not attuned to his demands.

“Your suggestion is not right,” the United boss. “He’s fitting in, he’s very motivated to put things right.

“I know which effort he is putting in. He’s totally with us.

“So, he makes 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.

“So, he makes one mistake but also, off the pitch, what he is doing, how he lives, and I’m sure he is doing everything right to help the team to perform and to let us win.”

Ten Hag can ill afford any distractions right now but it was notable how much public backing he showed Rashford despite his clear annoyance at his post-derby decision.

“He has to be as close as possible to the opponents’ goal, because there are his qualities,” he said.

“There he is so important for us and he will contribute so much to our success.

“We have to get him there as a team and he, as an individual, also he has to make his movements to arrive in the right moments, so his timing is right and I’m sure he will be back.”

How the Red Devils and their manager could do with Rashford getting back his scoring touch at Fulham on Saturday lunchtime.

The midweek loss to Newcastle was their eighth defeat in 15 matches in all competitions, making this United’s worst start to a season since 1962-63.

That run has led to scrutiny and speculation about Ten Hag’s position, but the “fighter” will not give up on a job that nobody has able to successfully fill since Sir Alex Ferguson left in 2013.

“It’s possible, I’m convinced (United can be successful),” the defiant Dutchman said.

“Sometimes you have difficult periods and when you stick together – and we are together – then we come through these difficult periods.”

Asked whether the structure is right for club to be a success, Ten Hag said: “I wouldn’t work here if I thought it wasn’t right.”

All the focus right now is righting the United ship before November’s international break, with games against Fulham and Luton bookending the crunch Champions League clash in Copenhagen.

“Always, when the team is not playing well, you think about it, to get it right,” Ten Hag added. “I’m not thinking about things away from the team.

“Of course, sometimes I need my relaxation to get energy, but for now it’s 24/7. You think about ‘how do I get this right?’”

Meanwhile, midfielder Casemiro has been ruled out for “several weeks” with a hamstring injury.

After missing three matches, the 31-year-old captained Ten Hag’s side on his return against Newcastle in the Carabao Cup on Wednesday.

Casemiro was replaced at half-time of the 3-0 defeat and United have now confirmed he will miss a key run of fixtures.

The club said in a statement: “Casemiro will be out for several weeks due to a hamstring injury suffered during our Carabao Cup defeat to Newcastle United on Wednesday.

“The Brazilian midfielder was withdrawn at half-time due to the issue, and subsequent assessment has revealed a strain that will keep him out for a number of weeks.”