United States international Timothy Chandler is to undergo surgery and will be out "for the foreseeable future" after suffering a lateral meniscus tear during Eintracht Frankfurt's 2-2 draw with Borussia Dortmund on Saturday.
Chandler went down without being touched by an opponent 10 minutes before half-time against Dortmund and had to be replaced by Carlos Salcedo.
Frankfurt announced on Monday that tests have shown the 27-year-old will require surgery "after suffering a lateral meniscus tear in his right knee."
A statement on the club's official website added that they "will be without first-choice right-back Timothy Chandler for the foreseeable future."
While the defender had played every minute of Frankfurt's Bundesliga campaign this season, he was not selected by then-United States head coach Bruce Arena as the nation failed to qualify for the 2018 World Cup earlier this month.
Stephan Uersfeld is the Germany correspondent for ESPN FC. Follow him on Twitter @uersfeld.