Sancho has signed a five-year contract with United after completing his £73million move from Borussia Dortmund.
The 21-year-old becomes the second most expensive English player of all time behind his new team-mate Harry Maguire and United have confirmed his shirt number.
The club said: “Manchester United can confirm that new signing Jadon Sancho will wear the No25 shirt, after joining the club on a five-year deal.”
The last player to wear the No25 for United was Odion Ighalo during his loan spell at Old Trafford between 2020-21.
But perhaps the jersey is most often associated with Antonio Valencia, who wore it for all but two of his 10 seasons at the club.
Sancho has said he is “honoured” to have joined United and insists he is ready to take a bigger step and help bring trophies back to Old Trafford.
“It’s an honour,” he said. “Growing up, Manchester United was one of the biggest clubs that everyone knows, and of course there is also all the trophies they’ve won.
“That’s one of the reasons why I came to Manchester, because I can see the development that’s going on here and I want to be a part of it, especially because it’s such an iconic club and being part of it is kind of a dream come true.”