Real Madrid midfielder Sami Khedira tore the anterior cruciate ligament in his right knee during Germany's 1-1 friendly draw with Italy on Friday and will likely miss the rest of the season.
The injury was sustained in a tackle on Italian midfielder Andrea Pirlo in the second half.
The German football federation said it still hopes Khedira will be fit in time for the World Cup in Brazil.
Germany coach Joachim Loew says "it's a bitter blow for Sami and for us all. He is a great fighter, on and off the pitch. He's always positive. That will help him and so I'm optimistic that he'll be fit again before the World Cup kicks off in Brazil."