Reports have suggested Jose Mourinho's new £32m signing could be out for up to six weeks after pulling up with a hamstring injury in training.
But the Blues will put the former Atletico Madrid forward through further assessments before making any prognosis.
Costa has made a fine start to life in the Premier League, scoring in wins over Burnley and Leicester.
With Fernando Torres in talks over a proposed move to AC Milan and Didier Drogba the club's only other senior striker, Mourinho could make another move into the transfer market before Monday's deadline.
Roma forward Mattia Destro continues to be linked with a switch to Stamford Bridge.
Watch Chelsea's Premier League clash at Everton live on Sky Sports 1HD on Saturday Night Football, with coverage underway from Goodison Park at 4.45pm.