Schalke will have to make do without the services of Klaas-Jan Huntelaar for "several weeks" due to a knee injury.
The Netherlands international suffered the knock in Schalke's final training session ahead of Saturday's Revierderby against arch-rivals Borussia Dortmund and consequently faces a spell on the sidelines.
"Ligament injury during our final training session: Schalke will be without Klaas-Jan Huntelaar for several weeks," a brief statement on the club's Twitter account read.
"Get well soon, Klaas-Jan."
Huntelaar's injury will come as a major blow to head coach Markus Weinzierl ahead of the highly-anticipated clash with Dortmund at Signal Iduna Park, with Breel Embolo also unavailable due to a serious ankle injury.
The absence of Huntelaar and Embolo means Weinzierl is likely to give Franco Di Santo the nod up front in the coming weeks.
Huntelaar, 33, has netted three goals in 10 appearances in all competitions this season.