The injury means he will miss the USMNT's upcoming summer schedule, including the CONACAF Nations League, Gold Cup, and the Olympics. He faces a tight schedule to recover in time for the squad's first World Cup qualifying games in September.
Swansea manager Steve Cooper said postmatch the injury "does not look good" and scans revealed that Morris has suffered a serious knee injury.
"He's had a bad injury unfortunately for him," Cooper said of Morris. "It's significant ligament damage, ACL. Everything we hoped it wasn't, unfortunately it is."
Morris moved to Swansea on a five-month loan deal in January -- the club had an option to sign him on a permanent deal from Seattle -- but the injury means his season is finished at the Championship side. Morris made five appearances for Swansea -- four in the Championship and one in the FA Cup.
A Seattle native, Morris has tallied 35 goals and 20 assists in 105 games (96 starts) with the Sounders since making his MLS debut in 2016. Morris missed a year of action after tearing the ACL in his right knee in February 2018.
Internationally, Morris has been a mainstay with the U.S. men's national team with 10 goals and eight assists in 39 caps. He scored the Gold Cup-winning goal against Jamaica in 2017.
"It's the end of his season for us and a long road back to recovery, it's very cruel," Cooper added. "It's a cruel injury anyway, but in the circumstances of him fulfilling an ambition and coming to Europe and being a part of what we're trying to do here. It's a really tough one for him and us to take.
"He has our support of course, I'm not quite sure of the next steps of his recovery whether it's here or back home in the U.S."