Schalke management fear Sepp van den Berg has suffered a serious injury.
Liverpool loanee collapsed during the game against FC Augsburg (2:3) and was forced off.
Van den Berg has a suspected serious ankle injury.
Following the match, Schalke chief Rouven Schröder revealed that the Dutch centre-back is likely to have collected a serious injury.
The sports director told DAZN that he had "heard something about a break".