Chelsea boss Jose Mourinho has revealed his concern about the extent of striker Diego Costa's persistent hamstring injury.
Costa, 26, has been dogged by hamstring problems for 18 months and was restricted to 24 Premier League starts in his debut season for Chelsea.
The Spain international still managed to plunder 20 league goals as Chelsea marched to the title, but his injury ills show no sign of clearing up. He is some way short of fitness ahead of the Blues' opener at home to Swansea City on Saturday evening.
Mourinho explained that the medical staff have additional concerns as the injury is not showing up on scans, meaning the club have no idea when he will be 100 percent again. He played no part in Wednesday night's 1-0 defeat at home to Fiorentina.
"Costa is not ready. It is not a good feeling for him, it is not a good feeling for me," Mourinho told reporters. "I have to be honest and say that it is a bit of a concern.
"A player that didn't finish the season and [then] doesn't start the season obviously doesn't make me happy.
"The boy is trying hard but he has a problem against Barcelona [International Champions Cup last Tuesday]. The scans show there is no injury so next day he trains, but the next day [after that] he is not comfortable.
"Then, 24 hours before the game [Community Shield loss to Arsenal], we don't know if he plays or doesn't play."
It means Mourinho must consider bolstering his forward line with only Radamel Falcao, who has a question mark hanging over him after an indifferent loan spell at Manchester United last season, and Loic Remy in reserve.
He added: "In this moment, the only thing I want to do is play against Swansea. The squad is good enough and big enough to play against Swansea."