The Dane acknowledges the emotional highs experienced during the cup run - as well as reaching the 40-point mark - may be having an effect as the campaign draws to a close.
"Fatigue could be a factor for some players. We cannot exclude that," he said.
"For some players it has been their first year in this team, whether they have come from abroad or from the youth team like Ben Davies.
"Jonathan de Guzman did not play much last season and he has played a lot of games this season, as have Pablo Hernandez and Michu.
"But, as well as the physical side, there is the mental side.
"It is completely normal when you reach your target to relax and not be at as high a level as before, even if you do not mean to.
"It is something I have felt across the whole club. After winning the final and getting to 40 points against Newcastle, everybody took a deep breath.
"Everybody is saying 'what a great season you had', but it should be 'have' not 'had', because we are still playing."