Diego Costa has revealed he returned to pre-season training at Chelsea out of shape and that has contributed to his poor form this season.

The Spain international has failed to replicate his stunning performances of last term, managing just one Premier League goal in 2015-16 so far - a tally not helped by his three-match ban for lashing out at Arsenal defender Laurent Koscielny at Stamford Bridge on September 19.

Costa admits he only has himself to blame after a summer of indulgence.

He said: "I got injured at the end of the season and then I went on holiday.

"Maybe I got out of my diet and when I came back I was not the way I was supposed to be. I was a little bit overweight. That affected my game."

Chelsea's last game ended in a 3-1 home defeat by Southampton - after which beleaguered coach Jose Mourinho insisted the only way he would leave the club is if he was sacked.

The club have subsequently offered their public backing to the Portuguese and Costa insists the players also remain firmly behind Mourinho.

He added: "You can be selfish and blame it on the manager but I'm not going to do that. I'm responsible 100 per cent and so are the other guys.

"We need to blame the players because we came back from holiday very confident.

"We thought we could go back into the way that it was last season.

"Then, by the time we actually realised the situation we were in, the team was already in a bad position. All we can do now is train very hard, work very hard and try to get back to where we were last season.

"If you ask a million players who they want as their manager, they will all come back with a top three list of Mourinho, [Pep] Guardiola and Diego 'Cholo' Simeone.

"It was one of the reasons I joined Chelsea. You know when you have a manager that is always successful, is always in the title race and always playing in the Champions League.

"He is competing at the top level, he is going to help you develop and become a better player. And help you win titles in your career."