United are hoping to take the England international to Old Trafford but his £115million price tag is off-putting.
"I think it was very interesting you talk about the character of Sancho," Falk told the Football Ranks podcast.
"Bayern Munich was very interested in him too but they didn't get him because Dortmund form young players.
"Bayern Munich resisted because of that. I know the sporting director would have liked to do it anyway."
Dortmund have set United a deadline of August 10 to complete the deal for Sancho or else they will close the door and focus on preparing for the 2020/21 campaign.