Sanchez was even spotted taking selfies at Old Trafford last night wearing the No 7 shirt.
He will take the vacant shirt for the first time since Memphis Depay left the club and follow in the footsteps of same famous faces.
David Beckham, Cristiano Ronaldo, Eric Cantona and George Best have donned the famous number for Manchester United.
And Alexis Sanchez will hope to emulate those stars at Old Trafford in the four-and-a-half years he has signed for.
Sanchez is set to earn around £500,000 a week becoming the highest-paid player in the Premier League.
The 29-year-old was in Manchester over the weekend going through the formalities before the move.
And Henrikh Mkhitaryan was in London finalising his move to Arsenal.
The pair will swap places with no money being exchanged between the clubs.
Both clubs are expected to make the announcements today with Arsenal also chasing Pierre-Emerick Aubameyang.
Mkhitaryan will become Arsenal’s highest-paid player on just over £200,000-a-week.
The players could be set for their debuts this week with Manchester United taking on Yeovil in the FA Cup on Friday.
Arsenal meet Chelsea in the League Cup on Wednesday but Mkhitaryan will be cup tied but could play against Swansea next Tuesday.
The signing of Sanchez will be another major statement for United after the arrivals of Paul Pogba and Romelu Lukaku over the past two summers.
Ed Woodward has wanted an iconic No 7 since he joined United and Sanchez appears to be that man.
United have looked at Antoine Griezmann, Gareth Bale and Paulo Dybala, but have beaten rivals Manchester City to Sanchez.
The Chile ace has spent three and a half years at the Emirates winning two FA Cup and the Community Shield.