Chelsea have revealed that Diego Costa has suffered a "minor muscular injury", but will not confirm whether the striker will be out of action for a significant period of time.
Reports have suggested that the Spain international could be sidelined for six weeks after picking up a problem in training.
However, the club have attempted to calm fears over Costa's fitness by telling Sky Sports News that he will be monitored over the coming days after picking up a muscle injury.
Costa, who moved to Stamford Bridge from Atletico Madrid this summer, has scored two Premier League goals so far for the Blues, who have begun their season with a 100% record following two victories.
Jose Mourinho's side will face Everton at Goodison Park this Saturday.
