Analysis
BBC Sport's Simon Stone
Dortmund and Manchester United have reached an impasse over the fee.
The German club want about £100m for the player, including a large up-front payment. But United think that does not take into account the financial impact of the coronavirus pandemic.
The Old Trafford club, who meet FC Copenhagen in the Europa League quarter-finals in Cologne on Monday, have threatened to look at alternatives.
There has also been a suggestion Dortmund will offer Sancho a new contract.