The Croatian midfielder joined Chelsea previous year on loan from Real Madrid and impressed during his season-long stay at Stamford Bridge.
It is expected that Eden Hazard will wear the No.7 shirt at Real Madrid and the club's new kit is already on sale in Dubai with the Belgian superstar given that number.
He was then followed by Valencia, who was signed from Wigan as a right-winger replacement for Ronaldo in 2009 but switched from the No 25 shirt to No 7 for the 2012-13 season.
He scored one goal in all competitions, which was in the league, before returning to his old shirt because he 'had good times and good fortune in that shirt.
The Argentina forward scored twice in his first four games and a third at the beginning of October but then failed to net again in the league all season before moving on to PSG just a year after arriving.
United's number seven by default has often been correlated to the clubs most important player at any given time, and it is no surprise that it is the number five-time Ballon d'Or victor Cristiano Ronaldo wore during his hugely successful six seasons at Old Trafford.
Last, and by many means least, has been Alexis Sanchez.
Inter have swooped in to try and re-sign their former player and they have reportedly been in talks with Real Madrid to take Kovacic back to the San Siro this summer.
The Chilean has scored three in the Premier League, bagging just two more away from the league, and could be sold this summer.