United's busy run of fixtures continued with a 0-0 draw at Southampton on Wednesday, a clash which marked their fifth game this month.
And Mourinho insists his side's league outing should have been moved to Saturday as he asked for Palace manager Sam Allardyce to take it easy against what is set to be a youthful United team.
"I never saw any detail of trying to care about the English teams involved in European competitions," he said.
"I never saw that with Chelsea, I never saw that with Manchester United, I never saw that with Manchester City last year. I never saw. I never saw. So I think it's just a lost battle [asking to move the game].
"You have to accept the way it is and I hope the fans at Old Trafford on Sunday, they support the team, they forgive some naivety, they forgive some lack of confidence.
"I hope that Big Sam shows he's a good friend and they go slow. He tells [Wilfried] Zaha to go slow, he leaves [Christian] Benteke at home. I hope he goes soft on us."
Mourinho said the likes of Demetri Mitchell, Scott McTominay, Axel Tuanzebe, Matthew Willock, Josh Harrop and Zachary Dearnley would join Eric Bailly and Paul Pogba in the matchday squad.