The 30-year-old has not featured for the Bundesliga outfit since the club's 4-0 defeat to Wolfsburg in August, when the Netherlands international sustained ligament damage in his right knee.
Head coach Jens Keller had hoped to have Huntelaar available after the international break, but a training injury this week has curtailed his progress and Schalke must now wait to see if an operation will be required to correct the issue.
"Klaas-Jan Huntelaar suffered deterioration in his right knee after a training incident on Monday," a statement on the club's official website reads.
"This resulted in the 30-year-old having an MRI examination on Tuesday. Whether the injury is treated conservatively or surgery is necessary, all parties will decide in the coming days.
