Chelsea manager Jose Mourinho says he doesn't know if his striker Diego Costa will be fit to start in next Saturday's Premier League opener against Swansea at Stamford Bridge.
Costa missed Sunday's Community Shield at Wembley because of his recurring hamstring issues, with the Premier League champions missing the input of their leading scorer from last season in a 1-0 defeat against FA Cup winners Arsenal.
When asked whether he expected Costa to return in time to take his place in the Chelsea line-up against Swansea, Mourinho said he did not know whether the Spanish international would be fit by next weekend.
"Will Costa be fit for Swansea? I don't know," Mourinho told reporters. "You think I'm lying, but I'm not. Two days ago he was ready to play and yesterday he trained normal.
"He had a little problem after the Barcelona game [in Washington D.C. last week]. After that he was training normally and we thought he would be ready, but then he was feeling uncomfortable."
Mourinho has been keen to give his players an extended break this summer as they prepare for the new season, but that extra period of rest does not appear to have resolved one of the biggest issues that could undermine his side's title defence.
Costa started 24 Premier League games for Chelsea last season and scored 20 goals, but he was struggling for fitness during key fixtures in domestic and European competition, and Mourinho will be concerned that his fitness issues appear to be ongoing heading into the new campaign.