Valencia, on the shortlist for the Premier League's player of the month after an impressive start to the season at right back, will return to Manchester next Friday, United manager Jose Mourinho said.
"The day before Man City, we will still have Sergio Romero, Marcos Rojo and Antonio Valencia arriving," Mourinho told the club website.
"It will be a complicated process but we know it is like this when we have these players. And I would love all of the players to go because it would mean that everybody is being selected for their national teams."
Mourinho may be forced to play one of Phil Jones, Matteo Darmian or Timothy Fosu-Mensah should converted winger Valencia not be ready to face City.
Both Manchester clubs come into the fixture with 100 percent records from the opening three games of the Premier League season.
(Reporting by Toby Davis; editing by Ed Osmond)
