Chelsea midfielder Denis Zakaria has been ruled out for four weeks with the injury that he sustained in the Blues' midweek Premier League defeat to Fulham.
The Juventus loanee experienced a slow start to life in West London, but he had begun to force his way into Graham Potter's XI on a consistent basis thanks to a string of strong performances.
Zakaria was given the nod in the engine room alongside Mateo Kovacic at Craven Cottage on Thursday evening, but he only lasted 56 minutes before being withdrawn.
Chelsea ended up suffering a 2-1 defeat without Zakaria on the field, and subsequent tests have revealed a moderate quadricep injury for the Switzerland international.
Speaking to reporters after Sunday's 1-0 win over Crystal Palace, Potter confirmed that Zakaria would be forced to miss the rest of this month as Chelsea's injury crisis worsens.
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"Denis is going to be [out for] four weeks, top of his quad, so that's a blow for us. Hopefully, he can be sooner," Potter told a press conference.
Zakaria has one goal to show from nine games in a Chelsea shirt since making the loan move in the summer, having had to wait until November 2 to make his debut against Dinamo Zagreb in the Champions League.
The 26-year-old scored in his opening game for the club but did not make his Premier League debut until the 2-0 success over Bournemouth on December 27 - his first of four successive starts.
With Zakaria sidelined, an injury-ravaged Chelsea are now working without no fewer than 10 players through fitness issues or suspension, with Joao Felix serving the first of a three-game ban on Sunday after his sending off against Fulham.
Ruben Loftus-Cheek was back on the bench against Palace, but Zakaria's fellow midfielder N'Golo Kante is also out of contention alongside Wesley Fofana, Edouard Mendy, Raheem Sterling, Christian Pulisic, Ben Chilwell, Armando Broja and Reece James.
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Chelsea have the option to make Zakaria's deal permanent for a €33m (£29.2m) fee in the summer, although it remains to be seen if the Blues will take up that option amid the expectation of a midfield reshuffle.
Kante and Jorginho are both at risk of leaving on a free transfer after entering the final six months of their contracts, although both players are in talks with the club over renewals.
A winter move for Benfica's Enzo Fernandez is now off the cards, but Brighton & Hove Albion's Moises Caicedo continues to be linked with Chelsea, who have brought in Andrey Santos from Vasco da Gama this month.
However, the 18-year-old is yet to make a matchday squad for the Blues and is expected to head out on loan before the January window closes for business.
Kai Havertz's header propelled Chelsea to a much-needed win over Crystal Palace on Sunday, and Potter's side are next in action away to Liverpool next Saturday lunchtime.