Sancho has been asked to train alone pending a resolution between him and his manager.
Earlier this month, Sancho was not included in the Manchester United squad for the Premier League trip to Arsenal, with Ten Hag citing a lack of application in training for his exclusion.
Sancho hit back almost immediately, as he took to social media to issue a quick rebuttal to the claims made by his manager.
The 23-year-old will now spend some period away from the United first team until a solution is found.
A club statement issued on Thursday read: "Jadon Sancho will remain on a personal training programme away from the first-team group pending resolution of a squad discipline issue."
Sancho has made three substitute appearances in United's opening four league games so far this season.
He joined from Borussia Dortmund for £73m in the summer of 2021 but has scored just 12 goals in 82 appearances.
