Blues manager wants to see goals return for £32m striker.
Chelsea manager Jose Mourinho has admitted some concern over the performances of star striker Diego Costa, the Daily Star reports.
The Spanish international started the season on fire in front of goal, but now has just two in his last seven appearances for the Blues, who lost their first game of the season at Newcastle United this weekend.
Costa has struggled with injuries in his time at Stamford Bridge, and Mourinho feels his fitness his holding the player back at the moment.
“For me, the problem is not the goals,” said Mourinho. “They will come as a consequence of his condition. He has to improve his condition. He was injured and had many doubts because he went a long time without training.
“Obviously that must have an effect on a player in the way he runs, the way he moves and in his coordination.”