If Dortmund complete a deal before 10 June then he would be eligible to play in the Club World Cup, which also features his brother Jude’s current club Real Madrid.
Jobe Bellingham has made four appearances for England’s Under-21s and is in their squad for the European Under-21 Championship, to be held in Slovakia from 11-28 June.
England’s U21 boss Lee Carsley told BBC Sport that they would release players for the Club World Cup, which takes place in the United States from 14 June to 13 July.
“We’re supporting all of the players,” he said. “We have room within our schedule to make sure that they get a chance if they need to have a medical or they need to speak to a club. We support them with that.
“Ideally I want them here, of course I do. You want your strongest squad, but we have to put the players first and that is definitely what we are doing.
“I think it is something we have been preparing for. We always knew we would potentially lose two or three along the way.
“Fifa have precedence over our tournaments. If that is the case, with any of the players, their teams and their clubs will always come first in that competition.
“We have to make sure that we are agile and ready to adapt, hence why the first squad was a little bit bigger.”