Schalke boss Jens Keller has confirmed the Netherlands international will not return until 2014, regardless of when the 30-year-old decides to have knee surgery.
The 30-year-old Netherlands international had returned to training following his knee injury but suffered a setback Monday.
"It doesn't really matter what the decision is on Klaas-Jan Huntelaar," Keller said. "He can't play until Christmas. It doesn't matter if he decides to have an operation. He might recover without one. Both outcomes are possible. The decision has not been made yet.
"We didn't rush him back before he got injured. Usually an injury like his is fine after eight weeks. He felt good. He took part in everything and this setback was an accident. He collided with someone in a bad position. This would still have happened even if it was two weeks later."
The German club sits eighth in the Bundesliga after eight games and continues its campaign with a trip to Eintracht Braunschweig on Saturday.