Manchester United boss Jose Mourinho cited referee Michael Oliver's previous decisions against his side after they exited the FA Cup with a 1-0 loss at Chelsea on Monday.
United went a man down when Ander Herrera was dismissed just after half an hour for a second yellow card, and N'Golo Kante struck the only goal after 51 minutes.
Mourinho, who also was involved in a brief shouting match with counterpart Antonio Conte, at first tried to hold his tongue after the game about the decision to send off Herrera for two fouls on Eden Hazard.
"I don't speak. I just want to say that I'm really proud of my players, I'm really proud of Manchester United fans," said the former Chelsea boss.
"We have a very important match on Thursday [in the Europa League] and I want to try to rest a little bit, to try to prepare the team the best we can for the Thursday match."
But pressed further on the red card, Mourinho added: "I think we all watched the match until the red card and after the red card and then we can compare the decision of the two yellow cards in this case with other ones that were not given, but I don't want to go in that direction.
"Mr Michael Oliver -- a referee with fantastic potential. Manchester United were a bit unlucky. In four matches, three penalties and one red card in such an early moment of the game but again I cannot change that."
Mourinho was referring to the club's three Premier League matches that Oliver oversaw this year -- a loss at Watford and draws with Everton and Liverpool, each of which saw the referee grant United's opponents penalties.
The United boss approached Oliver after the game but did not bring up the red card. He said: "I shook his hand, I told him many congratulations. There is nothing to speak [about]."
Chelsea captain Gary Cahill said he thought his team showed the right attitude following Herrera's dismissal.
"We dug in and gave a good account of ourselves," said Cahill. "I thought it was a professional performance from us today, we controlled the game when we needed to.
"[The sending off] was early. It was a tough game for us today but obviously that turned it in our favour slightly after that. There were a few fouls leading up to that [the red card]. There were many fouls, no dangerous ones, but lots of niggly ones."
Cahill also paid tribute to man of the match Kante after the midfielder's goal proved decisive.
"He's been fantastic," Cahill said of Kante on the BBC. "You see what he did last season. He has come here and he has kicked on again.
"He's such a humble guy off the pitch, works hard. He's a tremendous addition to the squad and he's won us the game with a goal today, which is great."
Kante added: "It was difficult, Manchester United is a good team. It was a tough game. We are happy for the win."