Fabian Johnson left Borussia Monchengladbach's Europa League game with an apparent injury on Thursday, less than a week before he is expected to report to the U.S. national team for a pair of key World Cup qualifiiers.
Johnson came off in the 16th minute against Schalke and was replaced by Jonas Hofmann. There was no immediate word on his status.
The 29-year-old was named to Bruce Arena's U.S. squad to face Honduras and Panama over the international break that begins next week.
His loss would be a major setback for the Americans, who are already without injured right-back DeAndre Yedlin.