Chelsea have announced defender Thiago Silva suffered knee ligament damage during Sunday's 2-0 Premier League defeat at Tottenham.
The 38-year-old was forced off in the first half of the Blues’ loss to their London rivals and underwent a scan on his return to the club’s Cobham training centre on Monday.
Chelsea have not indicated how long the veteran Brazilian is expected to be sidelined for.
"Scan results have confirmed damage to Thiago’s knee ligaments and he will now work closely with the club’s medical department during his rehabilitation to return to action as soon as possible," a club statement read.
The loss of a key player is a major blow to under-pressure head coach Graham Potter, who has managed just two wins from Chelsea’s last 15 games in all competitions. They are currently 10th in the Premier League table.
Silva has featured in all but three of the Blues’ 24 top-flight matches this term, in addition to six of their seven Champions League fixtures.
West Ham goalkeeper Lukasz Fabianski is set for a long spell on the sidelines after suffering a horror facial injury.
The Polish veteran may require surgery after he sustained a fractured cheekbone and eye socket against Nottingham Forest on Saturday.
Fabianski's face collided with the knee of Forest defender Felipe and he was immediately substituted.
Manager David Moyes said: "We don’t quite know whether it’ll be operated on or healing itself, or a time-span at the moment.
"I’m waiting, but I couldn’t give you an answer. We’ve had the surgeon’s report back but I think there’s a decision to make as to whether it’s surgery or natural healing."
Fabianski joined West Ham from Swansea for £7million in 2018 and has made 164 appearances. But the 37-year-old will be out of contract at the London Stadium this summer.
"It’s huge for us and obviously huge for the goalkeeper as well," added Moyes. "At the stage of his career for him as well."
Alphonse Areola will now get the chance to stake his claim to be West Ham’s number one.
The 30-year-old, who was in France’s World Cup squad, has been limited to appearances in the cup competitions since arriving from Paris St Germain last year.
Areola will be in the Hammers’ line-up at Old Trafford on Wednesday night when they take on Manchester United in the FA Cup fifth round.
Danny Ings, who scored his first goals for the club in the 4-0 win over Forest, is cup-tied so Michail Antonio, who also found the net after coming on as a substitute, is set to start in attack.
