Antonio Rudiger will miss the rest of Chelsea's season due to a knee injury.
The Germany defender is now due to have an operation in Italy, having limped out of the Blues' 1-1 Premier League draw at Manchester United on Sunday.
Rudiger's loss, confirmed by the club on Tuesday, will prove a blow to Chelsea's bid for both a top-four Premier League finish and Europa League glory.
Fourth-placed Chelsea sit two points ahead of Arsenal with two league games to play, with the London rivals going head-to-head for the final Champions League qualification berth.
The Blues will face Eintracht Frankfurt in Thursday's Europa League semi-final first leg before hosting Watford on Sunday in their final home league game of the campaign.
Maurizio Sarri's men will take on Eintracht in the return leg at Stamford Bridge on Thursday week, before closing their domestic season with a trip to Leicester.
But now they must do so without key centre back Rudiger, with his absence likely to be covered by Andreas Christensen.
