Schalke could be without the services of Matija Nastasic for six months after the defender underwent surgery on a ruptured Achilles.
The Serbian international was forced off after just 17 minutes of Schalke's 3-0 victory over Werder Bremen on Saturday, and underwent surgery later in the day after the diagnosis of a ruptured Achilles had been made.
The club said on their official Twitter account: "What a blow! Matija #Nastasic has ruptured his Achilles' tendon & underwent surgery this evening. Get well soon! #s04."
The 22-year-old enjoyed a strong 2014/15 season with Schalke while on loan from Manchester City, and in June made the move permanent.