Chelsea defender Wesley Fofana has undergone reconstructive surgery on his anterior cruciate ligament.
The 22-year-old centre-back begins his rehabilitation at the Blues' Cobham training ground while the squad travel to the United States on a pre-season trip.
Fofana, who joined the Londoners from Leicester in 2022 for £75 million (€87.3m), featured just 15 times for Chelsea in the Premier League last season as he suffered a number of injury setbacks.
This latest problem comes two years after the Frenchman broke his leg in a pre-season friendly for Leicester against Villareal which saw him miss a large part of the 2021-22 campaign.
Thiago Silva, Trevoh Chalobah, Levi Colwill, Alfie Gilchrist and Bashir Humphreys are the remaining centre-back options at Mauricio Pochettino's disposal in the US as he prepares for Thursday's opening pre-season clash against Wrexham.
Meanwhile, Brighton have rejected a second bid from the Blues for star midfielder Moises Caicedo.
Chelsea's latest offer for the Ecuador international is believed to be around £70million.
Caicedo requested to leave Albion in January amid interest from Arsenal but in March signed a new contract until 2027.
The 21-year-old, who last season helped the Seagulls qualify for Europe for the first time and reach the semi-finals of the FA Cup, remains of interest to a number of Premier League rivals.
Caicedo joined Brighton from Ecuadorian club Independiente del Valle for a reported £4.5m in February 2021 before being loaned to Belgian side Beerschot.
He made his top-flight debut in April 2022 and has played 53 times during his time at the Amex Stadium, scoring two goals.
Chelsea and Brighton are scheduled to meet on Saturday in Philadelphia in a six-team Premier League pre-season tournament.
New Chelsea manager Mauricio Pochettino is in the process of overhauling his squad following the club’s worst season in almost 30 years.
Forwards Christopher Nkunku and Nicolas Jackson have already arrived at Stamford Bridge this summer, while Mason Mount, Kai Havertz and Mateo Kovacic are among a host of departures.
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