The Spain international, who became the most expensive player in the Red Devils' history after finalising his move on Saturday, is now set to make his United debut on Tuesday night against Cardiff City.
Mata was expected to take the iconic No. 7 shirt - worn by the likes of George Best, Bryan Robson, Eric Cantona, David Beckham and Cristiano Ronaldo - but the playmaker has instead been handed the shirt previously occupied by Anderson.
Anderson joined Fiorentina earlier this month on an initial loan deal, but the Brazilian midfielder is expected to sign for the Serie A outfit on a permanent contract this summer.
Wayne Rooney also previously wore Manchester United's No. 8 shirt, before switching to No. 10 in 2007.
Mata spent two-and-a-half seasons at Chelsea, winning the Champions League, Europa League and FA Cup.