The former world champion will not race again until January as he takes "a break for his head", according to Switzerland men's team boss Osi Inglin.
At Alta Badia on Sunday, Janka finished nearly eight seconds behind Ted Ligety in the giant slalom.
He will now focus on preparing himself for the giant slalom at Adelboden on January 12.
"At Alta Badia, he gave the impression he did not have any strength," Inglin said. "He will go back to work with his physical conditioning coach Peter Meliessnig and will have a check-up on his blood levels."
If those tests prove normal, Janka is expected to return to the slopes at Hinterreit in Austria on December 26 to practice his giant slalom technique with Tumler, Manuel Pleisch and Gino Caviezel.