The likes of Sami Khedira and Bastian Schweinsteiger have both missed large chunks of this season with respective knee and ankle problems, and Arsenal's Mesut Ozil remains out with a hamstring injury.
With the showpiece in Brazil a little over three months away, former goalkeeper Kahn - who won the Golden Ball for his performances at the 2002 World Cup, where Germany were beaten by Brazil in the final - has concerns over the impact those injuries could have on the squad.
"Half a year ago I would have immediately said that the national team has a big chance to win the World Cup," he told the German Football Association's official website.
"Of course there are Spain and Brazil, but our team was incredibly impressive in the qualifiers.
"The last tournaments and the successes of Germany suggest that we might get very far. On the other hand, the injured are a big problem.
"Khedira, Schweinsteiger, who was a long time injured, Ozil, (Marcel) Schmelzer, (Mats) Hummels.
"Especially with the great heat and the rigours of travel in Brazil, the coach has to wonder which players are fit for this tournament."
