That is the shock view of former Liverpool midfielder turned pundit Danny Murphy.
The ex-pass master believes that Mainoo may not be ideal for the double midfield pivot role in manager Amorim’s 3-4-3 formation.
"To play that role well, United's midfielders will need to be more than just mobile, too," he told BBC Sport.
"They will both have to love the defensive side of the game and be able to spot danger and then be fast enough to stop it. In the long run, I think Manuel Ugarte will be one of them.
"He needs a run of games to get his sharpness back, but we have seen glimpses of how good he is, for example, in the Europa League against Fenerbahce last month, and he has flourished under Amorim at Sporting before.
"As for who Ugarte will have alongside him, well, it will probably be someone who is not at the club at the moment. There is going to have to be activity in the next couple of transfer windows for them to get the type of player Amorim requires."
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