The Red Devils have a number of fitness and injury concerns with a day to go until the big kickoff, meaning that Mourinho may be forced to shuffle his pack.
Nemanja Matic, Antonio Valencia, Diogo Dalot and Marcos Rojo are all carrying injuries that will rule them out of the curtain-raiser, while the likes of Marouane Fellaini, Jesse Lingard, Ashley Young, Paul Pogba and Romelu Lukaku have returned late from World Cup duty.
Asked for an update on the eve of the game, Mourinho told MUTV: "No miracles. The players with a proper pre-season are fit and they are strong.
"For example, Alexis Sanchez had a good pre-season with lots of matches and lots of minutes. He's more than ready but you cannot have the players who arrived only last Monday after the World Cup semi-finals or final and three weeks' holiday. You cannot expect them to be fit."