The 29-year-old suffered an ankle injury in Bayern Munich's 1-1 draw with Freiburg, forcing him to miss his side's European Super Cup win over Chelsea before pulling out of Joachim Low's panel earlier this week.
The midfielder admits he is not certain how long he will have to spend on the treatment table but concedes the injury is worse than first feared.
"Unfortunately, I'm not as good as I thought," he was quoted as saying by Tuttomercattoweb. "I'll go ahead with some peace and quiet to recover at my best, but right now I can't even kick a ball.
"I hope next week I'll be better and I can return to training on the pitch."
Germany take on Austria on Friday before travelling to the Faroe Islands next week in the latest rounds of World Cup qualifiers.