Borussia Dortmund have set a deadline of Aug. 10 for a deal to be finalized. They won't listen to offers beyond that to avoid interrupting their preparations for the 2020-21 Bundesliga season, according to BBC Sport's Simon Stone.
A successful bid for the 20-year-old winger is expected to be worth as much as £100 million, and The Guardian's Fabrizio Romano reports that Manchester United are in "advanced" talks with Dortmund.
Although United have yet to submit a formal offer, the Premier League club would reportedly pay the fee in installments, Stone adds.
The proposed date would give Dortmund a little over a month to prepare for the new season, which kicks off on Sept. 18, without any distractions over Sancho's future.
And if United are successful, the Red Devils would get plenty of time to work with Sancho before the new Premier League campaign begins on Sept. 12.
Dortmund said last month they will be active in the transfer market if Sancho leaves this summer. Sports director Michael Zorc said the club had its sights set on "one or two players" before adding highly touted midfielder Jude Bellingham from Birmingham City in late July.
Sancho has evolved into one of the sport's brightest young stars since joining Dortmund from Manchester City in 2017. He ended last season with 17 goals and 17 assists over 32 Bundesliga appearances.