Sancho once played for United's rivals, Manchester City but left the club in 2017 to continue his career in Germany.
Player valuations around the world might drop in the light of the coronavirus pandemic.
Manchester United are reportedly concerned about how a big-money move for Jadon Sancho would look amid the Covid-19 pandemic.
The 20-year-old has been a revelation since his departure for the Bundesliga in 2017.
A 13-goal campaign last season has been blown out of the water this term, with Sancho's 17 goals and 20 assists catapulting Dortmund into a hotly-contested title race with Bayern Munich and RB Leipzig.
That has not stopped financial juggernaut Man Utd from registering their interest, however, with the forward's age and profile seeming to be a perfect fit for the new transfer policy to go younger and predominantly British at Old Trafford.