Schalke 04 captain Benedikt Hoewedes needs surgery on a fractured cheekbone and will be out for weeks after being injured in the 3-1 win over VfB Stuttgart that put them level with Bundesliga leaders Bayern Munich.
Germany international Howedes clashed with team-mate Marco Hoeger just before the break and was taken to hospital.
"They diagnosed him with a broken cheekbone," Schalke Sports Director Horst Heldt told reporters after Saturday's match. "He will undergo surgery on Monday."
The 23-year-old will spend the night in hospital and is expected to be sidelined for several weeks, said club doctor Thorsten Rarreck.
Schalke moved level on 37 points with Bayern, who slumped to a 3-1 defeat at Borussia Monchengladbach on Friday.