The striker has accepted he was out of shape at the start of the season and says it affected his game.
Chelsea striker Diego Costa has admitted he was 'overweight' after letting his diet slip over the summer.
The 27-year-old has scored just one goal in eight league games this season and blames himself for his lack of discipline.
"I got injured at the end of the season and then I went on holiday," the former Atletico Madrid forward said. “Maybe I got out of my diet and when I came back I was not the way I was supposed to be.