Napoli have confirmed that defender Kalidou Koulibaly sustained ligament damage during the 5-0 victory over Cagliari in Serie A on Sunday.
A Dries Merten hat-trick, coupled with further strikes from Marek Hamsik and Piotr Zielinski, handed Maurizio Sarri's side all three points, but the victory was marred by an injury to their star defender.
The club released a statement confirming the details of the injury sustained by the Senegal international, who is expected to be sidelined for roughly two weeks.
"Kalidou Koulibaly underwent medical tests this morning after the injury which forced him out of the match against Cagliari," the statement read.
"The tests showed elongation of the external collateral ligament in his left knee.
"The defender will undergo rehabilitation work in the coming days."
Koulibaly has been an ever-present figure in the side, featuring in 22 games in all competitions this season.