The Mirror says Dortmund insist Sancho will not be leaving this summer, after United refused to meet their £100million asking price for the forward.
Sancho is keen to make the switch to United and may now have to put in a transfer request to force a move, after Dortmund went public with their refusal to sell.
Dortmund and United are way apart in terms of an agreement over the fee for Sancho, with the latter only willing to go to £80m.
Sancho, 20, was convinced his future would have been resolved by now and that he would be a United player, with Dortmund having set an initial deadline of August 10 for any deal to be done.
But United's refusal to meet Dortmund's valuation meant England international Sancho had to fly to Switzerland with his team-mates to take part in a pre-season training camp.