Manchester United assistant manager Carlos Queiroz blamed the toll of international football for his side's defeat by Manchester City.
City beat their rivals 2-1 after both clubs' fans impeccably observed a minute's silence to mark the 50th anniversary of the Munich air disaster.
"We believe the team was affected by international call-ups," said Queiroz.
"But talking about that would be an excuse. It was not our day. We didn't play well and need to accept that."
England's players are believed to have had two training sessions a day in Fabio Capello's first get-together as manager of the national team.
Portuguese winger Cristiano Ronaldo and Serbia centre-back Nemanja Vidic were also on international duty in midweek.
"It was really unusual to see a couple of our players playing so slow, without tempo and making mistakes," added Queiroz.
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"That's never happened before and if it is a coincidence we will let other people decide.
"The reality is that the players have been affected. Not only the English players but others like Ronaldo and Vidic were not so sharp."
Queiroz admitted that United had played well below their usual form.
"We didn't play in the right way. Manchester City were really difficult to play against because they were very organised and compact waiting for the counter-attack, which they did very well.
"Individual mistakes, collective mistakes and the way City played was, in my opinion, the explanation why we did not take three points.
"We lost a lot of duels and that was something strange for us."
Arsenal can now move five points head of United at the top of the Premier League table if they beat Blackburn on Monday. The Gunners then visit Old Trafford in the FA Cup on Saturday.
"Benjani was absolutely brilliant"
Queiroz hopes United will bounce back from this setback by beating Arsenal.
"I am really disappointed by the result. It is always a disappointing day for us when we lose but especially because it was an important day for us," he said.
"But we are going to prepare ourselves for next week and beating Arsenal."
City boss Sven-Goran Eriksson's side have struggled recently but the former England boss believes this result shows the quality of his players.
"I thought our team did a great job because lately we haven't played as well as the beginning of the season," stated the Swede.
"This was a very good answer that we are a good team. All the players did an extremely good job."
Eriksson was particularly pleased with Benjani Mwaruwari, who scored on his City debut following a move from Portsmouth.
He said: "Benjani was absolutely brilliant. He scored a goal, kept the ball and when United had the ball he worked and worked. He's strong and quick and I'm very happy to have got him."
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