They will take to the field with an added advantage.
After their dramatic comeback victory against Newcastle, Mourinho's men need a win desperately and only a win against a strong opponent like Chelsea can breathe life into the dressing room of the Red Devils.
Notably, only some United players are on international duty.
Most United players are not on international duty
It cannot be denied that Mourinho's side have been unpredictable this term.
Jose has been introducing squad changes regularly, but among the players who took to the field against Newcastle, most are on a rest during the international break.
This can help Mourinho field a full-strength at Stamford Bridge on October 20.
David, Pogba, and Lukaku are away, but will surely start against Chelsea.
Which United players will be fresh against Chelsea?
Matic, who pulled out of the Serbian squad, has two weeks to prepare for the trip to London alongside Juan Mata, who hasn't been selected by Spain.
Ashley Young and Ander Herrera will be fit to start as well, with both not taking part in international football this term.
Fellaini, who is away with Belgium currently, might start from the bench.
Chelsea have several players away on international duty
On the other hand, Sarri's Chelsea have numerous footballers playing international fixtures.
Eight among the eleven who played in their 3-0 win against Southampton are away.
The only players from Chelsea's squad, who are sans international duties, are Willian and David Luiz.
Though Chelsea are playing way more beautiful and effective football than United and are clear title contenders, this might be a disadvantage.