Voller insists Ter Stegen is the best goalkeeper available to Germany, but he must play regularly once he recovers from his back operation if he is to be guaranteed a place in their World Cup squad.
With Joan Garcia and Wojciech Szczesny regarded ahead of Ter Stegen at Barca, a January exit appears his only chance of making next summer's World Cup.
Voller told Sky Deutschland: "A goalkeeper like Ter Stegen deserves to play in the World Cup. (Oliver) Baumann has been very good these past few months as a substitute, but Ter Stegen should be the starting goalkeeper.
"I hope he plays again very soon. With Barcelona or another team, starting in January. That's very important right now. To return to the national team, he has to play.
"He knows he has a great opportunity, and if he comes back, he'll probably be our goalkeeper for this World Cup. I think it's something that benefits us all."