Everton, who lost 2-0 to Benfica in the Europa League on Thursday night, go into Sunday's league meeting with West Ham without injury victims Mikel Arteta, Phil Jagielka, Leon Osman, Victor Anichebe, James Vaughan and Phil Neville.
"Maybe we could look back and say Europe has been a hindrance to us," he said.
"I've tried not to have any regrets but the more and more games you play the more you realise that managers have talked a lot of sense in the past.
"It makes it very difficult to win the Premier League games when you have got midweek games.
"Maybe that's why the word rotation has been used quite a lot to try to make sure everybody is as fresh as they can be.
"I've always wanted to put out my strongest team but undoubtedly it could be having an effect on some of the Premier League results."
Everton are only two points above the relegation zone after collecting just three wins in 10 league games this season.
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