The Red Devils visit the Estadio Metropolitano on Tuesday in their first Champions League away game in three years, but they will miss two of Carrick’s first-choice stars when they converge on the Spanish capital.
United made a winning return to Europe’s top table with a 4-0 victory over minnows Sabah at Old Trafford, but the level of their opposition will increase monumentally when they taken on Diego Simeone’s Atleti.
There was concern when Shaw and Mainoo were not spotted in open training ahead of Tuesday’s fixture, and Carrick confirmed the worst ahead of the game.
Sidelined: Luke Shaw and Kobbie Mainoo
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“They've not travelled, both picked up issues in the game at the weekend so they're out,” the United boss said simply.
It leaves the Premier League outfit with a headache over who fills in at left-back, with Patrick Dorgu, the natural replacement, sidelined with a hamstring problem picked up on international duty with Denmark.
Noussair Mazraoui, who has also played on the left of defence, is also an injury doubt after he returned from Morocco’s camp with a knock that kept him out of the 1-1 draw with Tottenham last time out.
That leaves Diogo Dalot as the other option, with the Portuguese having played in that position a number of times for United.
It could mean another run-out for Leny Yoro at right-back, after the Frenchman was selected ahead of Dalot against Spurs.