"It doesn't look good, it looks like he had torn a ligament. We're waiting for a full diagnosis, but it looks like he will be out for a while," admitted Low after Germany's 5-1 win in their final World Cup qualifier.
The centre-back pulled up with what looked like a thigh injury on 36 minutes and hobbled off the pitch, helped by Germany's medical staff.
It was a costly first half for the Germans in Kaiserslautern as Bayern Munich defender Niklas Suele also went off with a leg injury in the opening 45 minutes.
Germany secured their place at the 2018 World Cup in Russia with an away win against Northern Ireland last Thursday.
They finished their campaign with a perfect record after beating Azerbaijan to claim a historic 10th straight win in World Cup qualifiers.
It is the first time a German team has achieved the feat and the world champions are unbeaten in their last 16 games.
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