Borussia Moenchengladbach forward Luuk de Jong is set to be sidelined for up to six weeks following a kick from Marseille player Joey Barton in Thursday's Europa League match.
The Dutch international underwent surgery on his left knee on Friday, after a bone oedema in his kneecap had been diagnosed. Barton's 64th minute challenge during Gladbach's 2-0 win had forced De Jong to leave the pitch on a stretcher.
De Jong, 22, signed for €12 million this summer as a replacement for Marco Reus, had just begun to find his form in recent games, but could now miss the rest of 2012.
In his absence Gladbach turned their away match in Hannover around and ended the Lower Saxons unbeaten run of 22 home games.
The Foals came back from a 0-2, scoring three goals within nine minutes, a remarkable turnaround from their two last matches on the road in which they were beaten 5-0 by Borussia Dortmund and 4-0 by Werder Bremen.
"It shows, you have to keep fighting until the end," general manager Max Eberl said afterwards. "After the 0-2 and the prior knowledge of what happened in Dortmund and Bremen, everyone thought: 'Oh my god, what will happen today?' But the team showed a fantastic reaction."