United last week completed a £72.1 million deal to sign Sancho from Borussia Dortmund.
It is now understood that Sancho's announcement was delayed due to his 'desire' to be given the No.7 jersey.
Sancho was immediately handed that number when he signed for Dortmund from Manchester City in 2017.
But Solskjaer refused to ask Edinson Cavani to give up United's No.7 shirt to accommodate Sancho's request.
Instead, Sancho has taken United's No.25, which was free after Odion Ighalo left Old Trafford i n January.
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