United States midfielder Giovanni Reyna limped off in the 30th minute of Borussia Dortmund's match against Borussia Monchengladbach on Sunday with an apparent injury.
Reyna, who only just returned from a hamstring injury that kept him out six months, was replaced by Julian Brandt.
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The 19-year-old injured his hamstring in the first World Cup qualifying match for the U.S. against El Salvador on Sept. 2, and had played three times for Dortmund across all competitions since returning, including Sunday's start.