Chelsea's Nkunku ruled out for 'extended period' after knee surgery

Chelsea's £52m summer signing Christopher Nkunku has been ruled out for an "extended period" after undergoing knee surgery.

The French 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.

"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,