United States international Terrence Boyd is facing a lengthy spell on the sidelines after tearing his anterior cruciate ligament.
The RB Leipzig forward sustained the injury during his team's 1-0 defeat at home to Ingolstadt on Sunday in Germany's second tier.
The club announced on their official website that Boyd is to undergo surgery in the coming days and faces several months on the sidelines.
The 23-year-old had been RB Leipzig's marquee signing when joining from Rapid Vienna in the summer, but he has made limited impact, having just returned from a partial tear to the same ligament, which he suffered during a preseason friendly against Queens Park Rangers in July.
The club added on its website: "Get well soon, Terrence! You have our full support once again and you will come back again as you are a fighter!"
Boyd, who previously played with Borussia Dortmund's second team, had been in Jurgen Klinsmann's preliminary USMNT squad for the 2014 World Cup.