Chelsea will be without Christopher Nkunku for an extended period after the striker underwent knee surgery. 

The news is a huge blow for Mauricio Pochettino's Blues ahead of their Premier League opener against Liverpool at Stamford Bridge on Sunday.

Nkunku, 25, was injured during the club's final pre-season outing against Borussia Dortmund in Chicago last week, which finished 1-1 thanks to a late Mason Burstow equaliser.

The Frenchman, signed from RB Leipzig earlier this summer in a deal reportedly worth £52million, left the pitch in the 22nd minute following a knock to his knee in a challenge with Mats Hummels.

In an official statement, Chelsea said: "Nkunku has sustained a knee injury which will rule the forward out for an extended period. 

"He has undergone an operation and will now begin a rehabilitation programme with the club's medical department."

Nkunku impressed during Chelsea's tour of the United States, scoring three times. 

But it is not the first time the versatile attacker has been hampered by injury. 

The former Paris Saint-Germain ace missed the 2022 World Cup after suffering a blow to his knee in a 50-50 challenge with France team-mate Eduardo Camavinga while training. 

Nkunku did not return to action with Leipzig until February, although he still finished as the Bundesliga's joint-top scorer with 16 goals from 25 appearances.

Pochettino must now rely on fellow summer signing Nicolas Jackson to lead his attack. 

Armando Broja missed the trip to America to remain at Cobham to step up his rehabilitation following a serious knee injury sustained last term. 

Poch will also be able to call on the likes of Raheem Sterling, Mykhailo Mudryk and Noni Madueke but there is no hiding the fact the loss of Nkunku is a bitter pill to swallow.