John Brooks could miss Hertha Berlin's upcoming match against Schalke after sitting out training due to muscular problems.
Brooks, 23, was forced to miss Hertha's session on Tuesday and is now a doubt for the Bundesliga clash at home to the Royal Blues on Sunday.
"It's always difficult. It'll be a race against time for him," Hertha coach Pal Dardai said of the United States international to kicker.
Hertha come into the game sitting second in the Bundesliga table, having recorded two wins in their opening two matches, while Schalke are 17th after losing their first two.
With Brooks a doubt for Sunday's clash, Dardai is hopeful that former Bayern Munich player Mitchell Weiser will return in time.
The winger left Saturday's 2-0 win at Ingolstadt with a foot problem and Hertha were originally worried that he could be sidelined for a longer period.
"We've examined his foot. Nothing is broken, there is also no tear," Dardai said. "He could return to training soon."