Schalke could be without three of their star players ahead of their Champions League quarter-final, first leg at holders Inter Milan next week.
Christoph Metzelder, Mario Gavranovic and Peer Kluge are all doubts after being injured in their Bundesliga encounter against St Pauli on Friday.
Germany defender Metzelder broke his nose in the game, which was abandoned after a linesman was hit by a beer cup, but could potentially play with a face mask.
However, injuries to both 21-year-old forward Mario Gavranovic (ankle) and Peer Kluge (abdmominal muscle strain) in the match means the Royal Blues have a few concerns ahead of their trip to the San Siro.
Schalke coach Ralf Rangnick, who replaced Felix Magath two weeks ago, said: "At least with Chris we have the hope that he can maybe play with a face mask.
"But the success at St Pauli will make things a bit easier for us at Milan."