Valencia had previously worn the No.25 shirt, but has now been awarded with the number seven shirt previously worn by United greats such as George Best, Eric Cantona, David Beckham and Cristiano Ronaldo.
Valencia recently enjoyed arguably his most impressive campaign since joining United from Wigan. The Ecuador international was named United's Play of the Year, grabbing six goals in all competitions.
United new-boy Shinji Kagawa had been offered the number seven jersey following the departure of its previous owner Michael Owen, but rejected the opportunity and has now been handed the No.26 shirt vacated by Gabriel Obertan.
Meanwhile, United's other new signing Nick Powell has been handed Valencia's old No.25 shirt after completing his move from League Two play-off winners Crewe.
United are yet to confirm the remaining squad numbers for the 2012-13 campaign.