Maguire was substituted off during the goalless draw against Aston Villa before the international break due to a knee injury, while Mainoo was absent for England's two Nations League matches.
Elsewhere, Noussair Mazraoui, who underwent a minor procedure after experiencing palpitations, has returned to training with United alongside Alejandro Garnacho and Amad Diallo.
Meanwhile, Manuel Ugarte could be a doubt for United’s match on Saturday after he was forced off in Uruguay’s World Cup qualifier against Ecuador this week.
United have confirmed that the midfielder took part in a ‘recovery session’ on Thursday.
A statement from United on Thursday read: ‘Noussair Mazraoui, Alejandro Garnacho and Amad are all back in training after missing games for their countries during the international break.
‘Manuel Ugarte undertook a recovery session having just returned from international duty with Uruguay, and taking part in World Cup qualifiers.
‘Tyrell Malacia continued his progress towards recovery from long-term injury by participating in the first part of the group session.
‘Kobbie Mainoo and Harry Maguire were absent after picking up muscle injuries against Villa, and they are both expected to be out for a few weeks.
‘Mason Mount continues his recovery from a knock sustained against Tottenham Hotspur, and Luke Shaw from a muscle injury, with both making steady progress in their rehabilitations.’
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