Manchester United manager Jose Mourinho said their attitude in the 2-1 defeat at Huddersfield was worse than a friendly match.
Huddersfield took a two-goal lead in the first half, before Marcus Rashford’s late consolation goal.
United’s first loss of the season leaves them five points behind Premier League leaders Manchester City.
“When you lose a match because of attitude, that is really bad,” said former Chelsea boss Mourinho.
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United had kept seven clean sheets in their previous eight league games, but mistakes from Juan Mata and Victor Lindelof in the space of five first-half minutes were punished with goals by Aaron Mooy and Laurent Depoitre.
Despite almost 80% possession, United managed just three shots on target.
“I don’t even remember a friendly match when our attitude was so poor,” said Mourinho. “We could have a second goal and a draw but it would have been undeserved.
“I was a Manchester United supporter, I would be really disappointed because you can accept losing because the opponent had more quality, but not because the opponent had more attitude.”
Mourinho changes tack after Herrera interview
Speaking immediately after the game, Mourinho said he would not publicly criticise his players.
“I will analyse the game and, if I need to, I will criticise them,” he said.
When asked about the errors of Lindelof and Mata, the Portuguese said it would be “unfair to point fingers at players for individual mistakes”.
At the same time, United’s Spanish midfielder Ander Herrera gave television interviews and said that Huddersfield were “more passionate than us, more aggressive,”.
“When you play against a team that normally you are better than, you have to match their aggression and passion. We didn’t do that. It cannot happen again.”
Later, speaking to journalists in a news conference, Mourinho said: “I heard Herrera in his flash interview saying the attitude and desire was poor.
“Oh my God, when a player says that and feels that, I think they should all go to the press conference and explain why. Of course, it concerns me.”
United beat Benfica on Wednesday, their third straight Champions League win, but Mourinho refused to blame their defeat by Huddersfield on fatigue caused by their European exploits.
“We are happy to be playing in the Champions League,” he said. “These players have played European football for many years. We know other teams might have a week to prepare for league games.
“It is part of the game and not an excuse I want to use now”.
United travel to Swansea in the EFL Cup on Tuesday, before hosting third-placed Tottenham in the Premier League next Saturday, followed by the visit of Benfica on Tuesday, 31 October.