Real Madrid says Germany midfielder Sami Khedira has undergone an "arthroscopic revision" of his left knee.
The 27-year-old Khedira was already sidelined while recovering from a left hamstring injury.
Madrid did not say how long it expects Khedira to be out.
Khedira tore a right knee ligament last November and didn't play until May. He returned in time to help Germany win the World Cup in Brazil.