The Spaniard will be monitored by the Blues' medical staff to determine the extent of the problem, and no decision has yet been made on whether he will feature against Everton.Diego Costa has sustained a minor muscular injury in training and will be monitored by Chelsea's medical staff in the coming days.
Initial reports had suggested the Brazil-born Spaniard could be sidelined for up to six weeks after pulling up with a hamstring injury during a session at the Blues' Cobham training complex on Wednesday.
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Goal understands the exact extent of the problem - which is regarded as minor - has not yet been determined and no decision has been made on whether Costa will feature in Saturday's Premier League clash with Everton at Goodison Park.
Costa has made an impressive start to his Chelsea career, scoring two important goals in his first two Premier League matches against Burnley and Leicester City as Jose Mourinho's men collected maximum points.
Any prolonged absence for the 25-year-old would leave the Blues reliant on 36-year-old Didier Drogba and the out-of-favor Fernando Torres, who has recently been linked with a loan move to AC Milan despite Mourinho's public insistence that he will stay at Stamford Bridge.