Erik ten Hag has left the door open for Jadon Sancho to return to the Manchester United squad but says any comeback is "up to him."
Sancho hasn't played since August following a public row with Ten Hag and has been linked with a move away from Old Trafford in the January transfer window.
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A source has told ESPN that former club Borussia Dortmund are interested in re-signing the 23-year-old, possibly in a deal which could see Netherlands forward Donyell Malen moving the other way, but Ten Hag says there is a way back at United if he apologises.
"It is about a culture and every player has to match certain standards and it was about that," Ten Hag told a news conference on Friday.
"What will happen there, he knows what he has to do if he wants to return and it is up to him. He knows what he has to do, it is up to him.
"We will see what will happen. It is an internal matter, we will see what will happen."
Sources have told ESPN that it remains most likely that Sancho leaves the club in January because the England forward has shown no intention to apologise during his three-month exile.
Aside from the uncertainty around Sancho's future, Ten Hag says he's not expecting a busy January window.
"I don't think that a lot will happen in the window but we have to be prepared if there are opportunities," he added.
"If there are certain circumstances or surprises, we have to be ready to act."
One issue ahead of the window is the goalkeeping situation, with No.1 André Onana likely to be selected by Cameroon for the Africa Cup of Nations, which begins in the Ivory Coast in January.
Backup keeper Altay Bayindir is yet to make his debut for the club, and third-choice Tom Heaton, 37, hasn't played a Premier League game for nearly four years -- but Ten Hag hinted he is not looking to sign another goalkeeper.
"What we need is three very good keepers for a successful season and talent in the back, then the best situation is one or two keepers on loan because you have to develop them all the time," he said.
"We are pleased with the group we have now. We were aware of the situation and we have to manage that, so we have cover. We have a very strong keeper group, especially the first three. They can all play, they are all capable of playing at the highest standards needed. We are happy with the group and we are comfortable."