"Mendy was unlucky. In the last training session he had a little fracture of the bone. I think today (Monday) he is in surgery just to clean this little fragment of bone out," Ranieri told the club's website.
"It depends how long, it could be four weeks or five weeks. I don't know."
Ranieri confirmed forward Shinji Okazaki, who was not included in the squad for Saturday's league defeat at Chelsea, will be fit for Tuesday's Champions League clash with FC Copenhagen.
Despite struggling to mount a convincing defence of their English top flight title, Leicester, who are 13th in the league standings, have fared better in the Champions League, where they top Group G after winning both their games.
(Reporting by Ian Rodricks in Bengaluru; editing by Amlan Chakraborty)
