The Bundesliga giants have reportedly given United until August 10 to secure the signing of the England international.
But United are dragging their feet, as they are prone to do.
Lucien Favre is keen to know which players he will be working with ahead of the upcoming season.
But the Red Devils believe they will be able to seal a deal for Sancho beyond the mid-August deadline, reports the Manchester Evening News.
Dortmund want £100million for the 20-year-old, and United believe if they stump up the cash it doesn’t matter when they place the bid.
The complications with the deal lie in the structure, with United keen to pay a lower fee up front of around £60million with an extra £40m in add ons.
Sancho has been close to completing a move to Old Trafford for some time, but looks set to remain on that verge for a little while yet.