The development comes after the England international recently complained about his treatment in a social media post.

Sancho claimed he had been made a “scapegoat” after manager Erik ten Hag said he left him out of the squad for the game at Arsenal on September 3 because of poor performance in training.

United have confirmed the matter is now being treated as a disciplinary issue, with reports suggesting he was banished because he failed to apologise.

A statement from the club read: “Jadon Sancho will remain on a personal training programme away from the first-team group, pending resolution of a squad discipline issue.”

Sancho had gone on the offensive in response to Ten Hag’s comments after United’s 3-1 defeat in the game at the Emirates Stadium.

Ten Hag said the 23-year-old had not been included because he had failed to reach the levels expected of him.

“Jadon, on his performances in training we did not select him,” the Dutchman said. “You have to reach a level every day at Manchester United and we can make choices in the front line. So for this game he was not selected.”

Sancho responded later that day with an explosive statement on Twitter.

He wrote: “Please don’t believe everything you read! I will not allow people saying things that is completely untrue, I have conducted myself in training very well this week.

“I believe there are other reasons for this matter that I won’t go into, I’ve been a scapegoat for a long time which isn’t fair!”

The post has now been deleted but it remained visible for some days afterwards.

United, who have claimed six points from their opening four Premier League games this season, return to action after the international break as they host Brighton on Saturday.