U.S. striker Jordan Morris suffered a strained hamstring in the Seattle Sounders' 1-1 draw with the LA Galaxy on Sunday night.
The injury puts in doubt Morris' status for the national team's World Cup qualifiers against Panama and Trinidad and Tobago in October.
Morris, 22, pulled up near the hour mark after running after the ball and was replaced by Will Bruin.
Sounders coach Brian Schmetzer said his young striker will be further examined by his father, Michael Morris, the Sounders' chief medical officer.
"We'll take a look at it -- there's nothing we can do about it tonight," Schmetzer said.