Sancho is understood to want a return to England having left Manchester City three years ago, but would command a fee north of £100million.
Hamann says the time is right for Sancho to leave Dortmund.
"There will continue to be a market for the top players, like Jadon Sancho – he's just too good to wait another year," he told Bild.
"I see him going to the Premier League. The most likely option there is Manchester United."