Up to six Royal Blues players have been the victim of what appears to be a viral infection that has seemingly swept through the entire team ahead of the trip to Augsburg
Bild reports that as many as six first-team players, including Jefferson Farfan, Lars Unnerstall, Sergio Escudero and Ciprian Marica were all absent during training on Wednesday, as well as Teemu Pukki and Peer Kluge, both of whom only managed to shake off the ailment while in action.
It has been suggested that the infection sweeping through the Royal Blues' squad could be a bout of gastroenteritis, and defender Christoph Metzelder admits the illness has spread throughout the locker room like a plague.
"The accumulation of cases is enormous," the stopper told Bild .
"We still have to play in Augsburg on Sunday, but we must be careful that there are no more stumbles this season.
"The sick are just staying at home, so that no other players get infected.
Kick-off at the SGL Arena on Sunday is scheduled for 15:30CET, as the Gelsenkirchen club hope to extend their grip on third place in the league.