Borussia Dortmund star Giovanni Reyna may be set for more injury distress as he hobbled off after just 30 minutes on Sunday.
The U.S. men's national team attacker was making his first start since August after recovering from a hamstring injury sustained while on national team duty.
But he could be looking at more time on the sidelines now after this latest setback.
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Reyna went into Sunday's clash with Borussia Monchengladbach having played just twice for his club in the last six months, in cameos off the bench against Bayer Leverkusen and Rangers.
He had finally been cleared to play from the off, with Dortmund needing a win to stay within six points of Bundesliga leaders Bayern Munich.
All seemed to be going to plan for Reyna and BVB, who took the lead after 26 minutes through Marco Reus.
Following the team's celebrations, however, it became clear that the youngster was in some discomfort as he went down to the ground.
The decision was eventually made to take him out of the action, and Reyna limped off in tears to be replaced by Julian Brandt with less than half an hour on the clock.
The bigger picture
Reyna has proved a revelation at Dortmund since joining their academy from New York City FC, and became the youngest American to debut in the Bundesliga when he made his bow at the start of 2020 aged just 17 years and 66 days.
He has since become a fixture in the BVB line-up, missing just two Bundesliga games in 2020-21, but injury has cast a shadow over this term.
Sunday's game was just his fifth appearance in the league, and Dortmund will hope he has not sustained serious damage as they hope to recover his sparkling talents for what remains of the 2021-22 campaign.