The Portuguese coach has revealed that only four first-team players will be rested ahead of Wednesday's third-round tie with the Championship outfit - David de Gea, Antonio Valencia, Nemanja Matic and Eric Bailly.
Pressed on whether he is taking the game seriously, Mourinho told the official Red Devils site: "Oh yes, serious because it's football you know, it's football, it's competition, we take it seriously. Of course I'm not playing De Gea or Bailly but if we go to the next round probably these guys play and I give rest to others.
"Our squad is good but we don't have 30 players. We have what we have and a couple of injuries so we need some of the players that played [against Everton] to play and we need some to be on the bench because we need a strong team.
"I know the quality of the Championship and I know if we don't take the game seriously we are going to lose."