Damien Duff is unlikely to play again this season after dislocating his shoulder in training.
Duff missed more than three weeks in December with the same injury
The winger was ruled out for three and a half weeks in December when he suffered the same injury.
That means he is almost certain to miss the second leg of the Champions League semi-final aginat Monaco on Wednesday.
Irish international Duff had only just returned to training after missing three games, including the first leg against Monaco, with a virus.
The club website reported that Duff will have the problem assessed before deciding on the best course of action.
As well as the Monaco encounter, Duff is likely to miss Chelsea's final three Premiership games against Southampton, Manchester United and Leeds.
His most natural replacement is Danish international winger Jesper Gronkjaer.
Chelsea, 3-1 down from the first leg against Monaco, have already lost Claude Makelele and Marcel Desailly to suspension for the return at Stamford Bridge.
The club will hear on Friday if their appeal against Desailly's suspension for elbowing Fernando Morientes has been successful.
On a more positive not for Chelsea, keeper Carlo Cudicini has returned to full training.
The Italian suffered a broken bone in his hand during training in mid-March and has not played since.
Right-back Glen Johnson is also back in contention after an ankle injury, while Scott Parker is hoping to return in Saturday's game against Southampton after a hamstring problem.
Defender William Gallas has recovered from the same virus as Duff picked up as well as a hamstring injury.
However, Celestine Babayaro, Emmanuel Petit and Juan Sebastian Veron are ruled out.