Frank Lampard has confirmed Fiyako Tomori will miss Tuesday's Champions League clash with Lille.
The Blues must beat Lille at Stamford Bridge to book their spot in the knockout stages.
But they will have to do so without Tomori, who is dealing with a hip injury.
Lampard said: "The other news I suppose is that Tomori is out.
"He's got a small tiny strain around his hip area and it's been bothering him so I've taken him out for a few days."
However, in good news for Lampard, Antonio Rudiger is available for selection.
The Englishman added: "Potentially [it will be] difficult [for him] but our guard against that was to give him a lot of work," Lampard told reporters when asked for an update on Rudiger's condition.
"We've managed to create some things behind the scenes here in training that look like matchplay.
"He's done some pure running as well to be fair and he's come through all that. You can only speak as you look at him and he looks fit and ready to go. I know he's hungry.
"In terms of building him up, probably rightly so.
"He's a good defender. I think maybe people have overlooked the fact that we had... everybody spoke about youth at the start of the season, all these things and transfer bans.
"The idea that we started with five big players all injured for a period of time and carrying on that now, Rudi is back and Ruben [Loftus-Cheek] is a big player for us as well.
"You do miss those individuals so let's see what he can add to us now."