The France forward, who joined from RB Leipzig, suffered the injury in Chelsea's final pre-season game against Borussia Dortmund in Chicago, and the club have confirmed he will be missing for a significant spell of the new season.

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

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"The 25-year-old has undergone an operation and will now begin a rehabilitation programme with the club's medical department."

Nkunku's absence is a blow for new manager Mauricio Pochettino, who is preparing for Sunday's opening Premier League match against Liverpool, live on Sky Sports.

Pochettino has said he would be "open" to another addition to the forward department before the end of the transfer window.

Nkunku has been sharing striker duties during the club's pre-season tour of USA with £30m signing Nicolas Jackson, with both finding the net during a successful Premier League Summer Series campaign in pre-season.

Jackson and Armando Broja are now Pochettino's only available first-team strikers for the start of the new season.

Chelsea's opening Premier League fixtures

August 13: Liverpool (h) - kick-off 4.30pm, live on Sky Sports

August 19: West Ham (a)

August 26: Luton (h)

September 2: Nottingham Forest (h)

September 16: Bournemouth (a)

September 23: Aston Villa (h)

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