Maurizio Sarri felt tiredness was the reason for Chelsea’s poor first-half display in their 3-0 win against Watford.
The Blues, who faced Eintracht Frankfurt in the Europa League semi-final first leg on Thursday, were fortunate to be on level terms at half-time against the Hornets.
But they scored twice in quick succession after the interval as Watford faded.
“I think in the first half we were in trouble because we were tired – physically and mentally,” said head coach Sarri.
“Then in the second half they lowered their intensity and so we went in control of the match.
“We were lucky of course because we scored after two minutes and after the first goal we probably improved mentally.
“We were able to play well for 30-35 minutes but in the first half we were in trouble. We were tired – I think more mentally than physically.
“It’s not easy to play after 60 hours. In the past, after a match away in the Europa League, we won only one match. So it’s not easy, not only for us but for every team.”
Sarri also confirmed that N’Golo Kante, who limped off after 11 minutes, suffered a hamstring injury and could miss the remainder of the season.