Germany and Real Madrid midfielder Sami Khedira's World Cup hopes hang in the balance after he was ruled out for around six months with a torn cruciate ligament suffered in Friday's 1-1 draw against Italy, team doctors said on Saturday.
Khedira, who also tore another ligament in his right knee during the incident, will undergo surgery.
"He will need to be operated on but we are hopeful he could be fit in time for the World Cup," team doctor Hans-Wilhelm Mueller-Wohlfahrt said.
Germany take on England at Wembley in another friendly international on Tuesday.
"This is a bitter setback for Sami. But he always thinks positively and that is why I am optimistic he will be ready and fit when the World Cup starts," coach Joachim Loew said.
Khedira had formed a superb holding midfield partnership with Bastian Schweinsteiger, who himself underwent surgery this week for a persistent ankle injury. Schweinsteiger is not expected to return before the end of the winter break in January.
Loew said he had decided to travel to London without captain Philipp Lahm, first-choice keeper Manuel Neuer and playmaker Mesut Ozil in order to give other players a chance.
"They are absolutely part of the main structure of this team and what is important for me now is to give other players in these key positions a chance to show what they can do against a big opponent like England," he said.
Central defender Per Mertesacker, however, will return after sitting out the Italy game with flu.
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