Jose Mourinho does not believe opponents Ajax should not be in the Europa League, insisting they are a "Champions League team."
Ajax started the season in the Champions League qualification rounds before a two-legged defeat to Russian side Rostov meant they dropped into the Europa League group stages, where United's campaign also started.
"They are a Champions League team; they come from the Champions League," Mourinho said.
"I always disagree with it, I think a team shouldn't play two European competitions in the same season.
"I think if a team goes to the Champions League and then doesn't qualify, they should go home, they shouldn't have the opportunity to play in the Europa League.
"I think the Europa League competition is for teams that go to the Europa League in the beginning, like us.
"We finished fifth (in last season's Premier League), we went to the Europa League. We started in the Europa League from the beginning of the season and had to fight (to get) where we are."
Like United, Ajax have also played 14 games in this competition so will be able to sympathise with the gruelling route to Stockholm that Mourinho has often referenced.
The Portuguese believes one thing such a schedule has done is foster a bond within his squad, which is why he is so keen for Zlatan Ibrahimovic and fellow injured players Ashley Young, Luke Shaw and Marcos Rojo to be present.
"Everyone goes," Mourinho said. "We have a few on crutches but everyone goes. (We have a) fantastic group of players, fantastic spirit since the beginning of the season - a difficult run, lots of matches, we spent more time travelling, playing, in hotels, than at home.
"Because 60-something (games) means 140 days in a hotel; half of the year we spent together and that is only possible when the spirit is amazing.
"So everyone is going be there, crutches for Young, Shaw, Rojo, for Zlatan, but we all go together."