With Palace having secured Premier League survival last week, nothing is riding on the clash and Allardyce accepts Mourinho's gripe.
Confirming that a raft of academy players will play at Old Trafford this weekend, Mourinho said: "I hope that Big Sam [Allardyce] shows he's a good friend and he goes slow".
"They could easily have changed it last week and said "We will give you the best chance to try to win the Europa League".
Manchester United will hand debuts to Matthew Willock, Demetri Mitchell Josh Harrop and Zachery Dearnley against Crystal Palace after manager Jose Mourinho confirmed a swathe of youngsters will feature in their final Premier League game.
Midifelder Marouane Fellaini is doubtful for Manchester United's last league game and next week's Europa League final after sustaining an injury in Wednesday's goalless draw at Southampton.
'When you look at Jose's fixture list this will be his 63rd game on Sunday. "I believe it is not by looking at them, but by looking at ourselves".
'That would happen overseas.
Why Liam Payne Doesn't Love Harry Styles' New Single
Overall, "Harry Styles" will impress listeners who are expecting an album different to what One Direction has released. He has worked with so many different producers and artists.
Allardyce is already without Andros Townsend for a fixture Mourinho says will be started by his 20-year-old third-choice goalkeeper Joel Pereira.
Such is the level of inexperience in Mourinho's likely starting line-up, the Portuguese openly asked Allardyce's Palace to "go soft" on Sunday.
Following the 2-1 defeat at White Hart Lane on Sunday, Mourinho said that Premier League football "is just matches we don't want to play".
Souness is the latest figure to play down Mourinho's claims about a heavy schedule after Ajax boss Peter Bosz yesterday said he had no right to moan because he had such a big squad.
United have trained at Carrington on the day before most Europa League games this season, with the exception of the matches at Zorya Luhansk and FC Rostov.
"We will play our 56th game next Wednesday", he said. "The most important thing is the group and the fans and we go there in Stockholm for the win".