Germany boss Joachim Low has revealed that he does not yet know the severity of the injury which has threatened Marco Reus's World Cup campaign.

The Borussia Dortmund ace hobbled off the field midway through a 6-1 warm-up win over Armenia on Friday night following an ankle problem.

Consequently, fears over the 25-year-old's fitness have grown ahead of the World Cup beginning next Thursday, and Low admits that he is in the dark over the full extent of the injury.

"I do not know how bad it is," he told ZDF television. "He is being examined as we speak in hospital and we will wait and see what comes out of it.

"A lot goes through your head at that moment and you just hope it is not too bad but then you see it swell up a bit. I hope the ligaments hold up.

"Until 24 hours before the first World Cup game, according to the rules, we can nominate someone else."

Germany kick off their campaign by facing Portugal on June 16.