Michael Carrick and his squad are due to travel to the Spanish capital on Monday afternoon, but the pair’s absence from the morning session at Carrington has left their availability in doubt.
Both players started United’s weekend draw against Tottenham Hotspur. Mainoo completed the match after missing England duty during the international break, when injury concerns and workload management kept him out of the national squad.
United are keen to manage the young midfielder’s minutes carefully, particularly given his importance to the team and the demands of the season. If he is unable to feature against Atletico Madrid, summer signing Carlos Baleba could be in line for his first start since joining from Brighton in a deal reported to be worth £70 million.
Shaw’s situation presents a separate problem for Carrick. United are already without Patrick Dorgu, who was injured while on international duty with Denmark, while Noussair Mazraoui is also sidelined and did not train on Monday.
That leaves the coaching staff short of natural left-back options should Shaw fail to recover in time. Diogo Dalot and Harry Amass trained, giving Carrick alternatives, although using Dalot on the left would require another adjustment elsewhere in the defence.
Leny Yoro impressed at right-back against Tottenham, raising the possibility that he could remain in that position while Dalot switches flanks. Such a reshuffle would be significant against an Atletico side known for its intensity and ability to punish defensive uncertainty.
Matthijs de Ligt also trained after being absent from United’s matches since November 2025. However, he is not expected to be ready to play against Diego Simeone’s side.
Manchester United had not made a final decision on Mainoo or Shaw by mid-morning, leaving both players’ involvement dependent on their condition and the club’s assessment before departure.
With important options missing across the defence and midfield, Carrick faces a late selection test before a demanding European fixture.