Jose Mourinho has admitted that he cannot guarantee Diego Costa will always be fit enough to play for Chelsea after the striker picked up an injury.

The Spaniard injured his hamstring in the build-up to the Community Shield, keeping him out of the 1-0 defeat to Arsenal at Wembley, and making him a doubt for the champions' opening match of the Premier League season against Swansea City.

Speaking at the Premier League launch, the manager told reporters: "Last week he couldn't play in the Community Shield game. He was not ready to be involved.

"I cannot reassure fans he will always be fit but I can assure them he is working well and hard and everybody around him is helping him.

"I don't like to cry or moan about players that don't play. But obviously in such a short squad like we have, then when somebody is missing I am not happy. But it won't be an excuse for me."

Costa scored 20 goals in all competitions for Chelsea last season, but missed time in the second half of the season with an ongoing hamstring issue.