The Bundesliga club had set a deadline of Monday 10 August and the beginning of their pre-season camp, which Sancho has now joined, but the deal remains deadlocked with talks ongoing.
United and Dortmund are still struggling to agree a figure on the up-front fee, although The Independent has been told there is as little as £10m in the difference.
The German club want a deal that amounts to €120m overall in Euro with all deferred payments taken in, but United feel that is unrealistic in the current Covid-conditioned market.
With Dortmund resolute, sources close to both the player’s camp and United believe Sancho may have to take matters into his own hands to get the transfer completed, and possibly even put in a transfer request.
The 20-year-old and his representatives have been reluctant to do that due to a good relationship with Dortmund, but there is a growing feeling they may have to talk to the club about the situation if they believe they are being unrealistically priced out of a deal.
That could reasonably be argued given that this is set to be a greatly suppressed transfer market due to Covid-19, and that it is set to remain the case indefinitely.
Sancho had previously been so sure he was due to leave during the close-season break that he had said his goodbyes to Dortmund staff, only to greet them again on Monday.
The feeling among all parties is now that “someone has to act” to break the stalemate.