Arsenal boss Arsene Wenger is concerned his players are looking tired after their 2-1 defeat at Liverpool.
Wenger's team have won only one of their last six Premiership games and trail leaders Chelsea by five points.
"Maybe we are suffering a little from fatigue and maybe our efforts with
nine men in the Champions League have left us tired," he said.
Wenger, whose team drew 1-1 at PSV, added: "We gave a lot against Eindhoven and that may have affected us."
And there was more bad news for Wenger when the Football Association confirmed on Monday that Patrick Vieira's booking at Anfield means the Gunners skipper will be suspended for the match against Chelsea on 12 December.
The caution was his fifth which rules him out for one game and that will fall on the eagerly-awaited title clash.
Vieira was already due to miss the Rosenborg game five days earlier, when the Gunners must attempt to qualify for the Champions League knockout stage, because he was sent off against PSV.
With Brazilians Gilberto Silva and Edu injured, Arsenal's midfield in those games will be based on 17-year-old Francesc Fabregas and 20-year-old Mathieu Flamini.
"It is a big disappointment for me to miss those games in what is a very important week for the club," Vieira said.
"When we are going through a difficult time like this, I have a big part to play and I will try my best. As a team we have to improve. It is up to us. If we really want it, we are going to do it.
"The quality and the hunger to keep the title is there. We know what we have to do."
Gunners skipper Vieira told the Evening Standard newspaper: "We're still hungry for the title. We know we played better at the start of the season. We need maybe a bit of togetherness to help us win the games.
"Three or four years ago, maybe, we would have won the game at Liverpool. We are disappointed because we wanted to start winning again."
Wenger, meanwhile, claimed he is not even thinking about that Chelsea match.
"I am not really too concerned about what Chelsea are doing, I am more concerned with us getting back on track," said the Gunners boss.
"We have to regroup and find our way back to our best form.
"We are not incisive enough. I do not think there is too much wrong but when you lose the errors are highlighted.
"I won't be making any major changes.
"I cannot put my finger on any individual who is not playing well and I always feel that it is better to bring in new players, especially young players, when we are winning games."
Wenger said his team's defeat at Liverpool was due in part to Liverpool's strength.
"Physically they were very strong and we couldn't compete in the challenges and that's why there was not enough support for the strikers," he said.
"I don't think we defended particularly badly but at the moment every mistake we make goes in and we don't look as sharp physically as we usually are."