After previously spending four years with Dortmund, Sancho returned to Signal Iduna Park in January, joining on a loan deal until the end of the season.
Sancho was allowed to leave Old Trafford after being frozen out of the Man United squad following a public falling out with manager Erik ten Hag.
In September, Sancho took to social media to say he had been made a "scapegoat" after Ten Hag claimed the attacker had been left out of a game against Arsenal due to his performances in training.
Sancho will have to accept pay cut to complete Man United exit
The 24-year-old refused to apologise for his social media comments and was subsequently sent out on loan to Dortmund.
Sancho has rejuvenated his career during his second spell with the German club, scoring three goals and three assists in 20 competitive appearances.
The Englishman has started all six of Dortmund's Champions League knockout games, helping the club reach their first European final since 2012-13.
Sancho is believed to be keen to complete a permanent move to Dortmund following a report that he is reluctant to stay at Man United even if Ten Hag is dismissed at the end of the season.
However, according to The Sun, Sancho will have to accept a mammoth pay cut if he is to convert his loan move into a permanent deal.
The report suggests the Bundesliga side will be unable to match Sancho's current salary which is believed to be around £275,000-a-week.
Man United name asking price
Even if Sancho accepts a reduced salary, the two clubs will still have to agree a transfer fee to make the move possible.
Man United are prepared to listen to offers, but will not allow him to leave for anything less than 75% of the £73m they paid to sign him from Dortmund in 2021
While it remains to be seen how much Dortmund are willing to pay, the club's sporting director Sebastian Kehl has admitted they will "try everything" to sign Sancho on a permanent deal this summer.
The Man United loanee provided an assist in the 4-0 win over basement side Darmstadt on the final day of the Bundesliga season.
Sancho and his Dortmund teammates will now begin preparations for the Champions League final against Real Madrid on June 1.