While Premier League rules state a player who started the season wearing a shirt number cannot make a change unless he is given special permission, it appears Ronaldo may get that exemption as he looks to wear his favoured No.7 jersey at United.
Edinson Canvani wore that No.7 shirt when he played for United at Wolves on Sunday, but he may now look to switch to the No.21 shirt - the number he wears playing for Uruguay - after Daniel James made a £25million move to Leeds United and freed up that number in the United squad.
As Ronaldo's CR7 brand is built around the number he has worn throughout his career, he would be keen to continue that at United and the Premier League have already him down as United's No.7 on their website.
Meanwhile, suggestions that United will profit from sales of Ronaldo shirts following his return to the can be exposed as a long-running myth among football fans.
Adidas agreed to a deal that sees them pay United £75million-per-season for a ten-year shirt deal to produce and license club merchandise, but they collect a vast proportion of the revenue from sales or products.
So while United will get a small cut of Ronaldo shirt sales, Adidas will be the big winners when it comes to the return of one of the world's greatest players to England's Premier League.
Ronaldo is currently training with the Portugal team in Lisbon ahead of their World Cup qualifier against the Republic of Ireland on Wednesday night.