Lisandro Martinez will take the No 6 shirt at Manchester United while fellow new signing Christian Eriksen will wear No 14 at Old Trafford.
Argentina international Martinez, whose £55million transfer from Ajax was completed earlier this week, takes the number vacated by Paul Pogba, who has moved back to Juventus.
The likes of Gary Pallister, Jaap Stam and Wes Brown have worn the No 6 shirt at United in the past couple of decades.
Danish star Eriksen, who was snapped up by Erik ten Hag after he left Brentford, will take the shirt formerly worn by Jesse Lingard. Prior to him, the No 14 was worn by Javier Hernandez and Alan Smith among others.
Martinez featured and Eriksen scored as United beat National League club Wrexham 4-1 in a behind-closed-doors friendly at their Carrington training ground on Wednesday.
Both will expect top receive further game time this weekend as United play Atletico Madrid in Oslo on Saturday and then Rayo Vallecano at Old Trafford on Sunday.
United open their Premier League campaign at home to Brighton on Sunday August 7.
Martinez is reunited with new United manager Erik ten Hag after they worked together in Amsterdam.
The coach converted him from a defensive midfielder to a centre-back during his time there but Martinez offers United options in several positions.
He said: 'I was with him for three years at Ajax and I know his style of playing. With him, I improved a lot to be honest.
'He's here in Manchester now, so again the opportunity was there and for sure he's very important in my career.'