The Red Devils are already thought to have agreed personal terms with the England international, who is supposedly in line to pocket a staggering £350k per week at Old Trafford should a deal go through.
United are understood to have officially tabled a £67m bid for Sancho earlier this week, but their approach was swiftly knocked back by Dortmund as they seek a figure closer to £80m.
According to The Athletic, Man United also had the idea of inserting a Ballon d'Or clause into Sancho's deal, which would be activated if the attacker finished in the top three in voting.
However, Dortmund reportedly had no interest in that proposal, with the Black and Yellow instead looking for add-ons related to team performance rather than Sancho's individual accolades.
The England international amassed 16 goals and 20 assists in all competitions last season, but he is fighting an uphill battle to start for the Three Lions in their Euro 2020 opener with Croatia on Sunday.