Sancho is on the verge of joining United with the two clubs in advanced talks over a deal that could reach an eventual £108million.
BILD says Sancho has now put pen to paper on personal terms and all that needs to be determined before the deal can go through is the structure of the transfer.
But when asked on Tuesday about United's move for Sancho, Ole Gunnar Solskjaer kept his cards close to his chest: "This transfer window is a long one. Every transfer takes its course. It is what it is, so if there is any news we will update you."
Dortmund are refusing to budge from their £108m valuation of winger Sancho, which would see them make a staggering profit having signed him for just £8m from United's arch-rivals Manchester City in 2017.