Both Manchester United and City need wingers, and Mitoma will be fit in both clubs, just that the player will be the one to decide which club he will prefer to join in the January transfer window, that is, if Brighton will be willing to let him leave in the transfer window.
A player will join a big and tough team, Manchester United only a big team, so Mitoma should be in Manchester City.
That will be bad news for Brighton but good news for Mitoma. He is being noticed by big clubs. His career could advance with big teams. Something that Brighton can hardly do. Mitoma should take the opportunity if Pep Guardiola makes an offer. Pep will make him improve even more. About the proposal Erik ten Hag, Mitoma should carefully think about it. His career could be as dark as the club Manchester United.
Rather than looking for a new winger, it's better for Manchester United to sign a new goalkeeper and few defenders. Their midfielder and striker already strong enough, so they just wasting their money to sign a new winger.
I don't think Manchester United needs to sign goalkeepers and defenders anymore, it's too wasteful, and the squad is becoming more and more fragmented. Now, what they need to do is understand each other throughout the match.