Seattle Sounders striker Jordan Morris has torn the ACL in his right knee and will miss the next six to nine months, according to a report from Fox Sports analyst Stuart Holden.
The Sounders did not confirm the extent of the injury on Saturday. A source told ESPN FC's Jeff Carlisle that Morris was still being assessed.
Morris was injured in the Sounders' first game of the year on Thursday, a 2-1 defeat to Santa Tecla in El Salvador in the CONCACAF Champions League.
The 23-year-old fell to the ground without being touched in the 85th minute and had to be helped off the field.
The game was played on artificial turf, but coach Brian Schmetzer said he couldn't blame the surface for the Sounders' defeat.
Morris was the 2016 MLS Rookie of the Year but only scored three goals in 2017. He missed the end of the MLS regular season after suffering a hamstring injury in September.
That ultimately prevented him from playing in the United States' final World Cup qualifiers as the national team failed to secure a place in Russia next summer.
However, Morris returned to come off the bench in the MLS playoffs, and started the U.S.'s friendly against Bosnia and Herzegovina last month.