Rossi's positive test was first announced by the Uruguay Football Association and later confirmed by LAFC.
On Thursday, ESPN sources confirmed that Rossi's teammate Brian Rodriguez also tested positive adding to a crisis ahead of the club's playoff game against the Seattle Sounders on Nov. 24.
Rossi was with the Uruguay national team during the just-concluded international window in which La Celeste defeated Colombia, 3-0, and then fell to Brazil, 2-0, in a pair of World Cup qualifiers. Rossi was an unused substitute in both matches.
LAFC said in a team statement that Rossi, who won the MLS Golden Boot as well as the league's Young Player of the Year award, will have to remain in Uruguay until he tests negative, and that defender Diego Palacios and midfielder Jose Cifuentes are in the same situation, having also contracted COVID-19 while on international duty with Ecuador.
"LAFC has confirmed that defender Diego Palacios, midfielder Jose Cifuentes, and forward Diego Rossi have tested positive for COVID-19 while with the Ecuador and Uruguay National Teams during the most recent November FIFA international window," LAFC said in a statement on Wednesday.
"Upon receipt of the positive results, the players entered self-isolation in their respective countries and will remain isolated and follow their local restrictions and protocol prior to returning to Los Angeles. Additionally, forward Brian Rodríguez, who has been with the Uruguayan National Team, continues to test negative at this time. His return to Los Angeles as well as his status for LAFC's playoff match against Seattle Sounders FC on Nov. 24 is still to be determined."
The positive tests mean that of the four LAFC players called up during the recent window, only Rodriguez avoided testing positive for COVID-19.
The announcement continues an eventful few weeks for the club. Three of the team's players tested positive over the past two weeks of the regular season. And LAFC thought all four of its international call-ups would miss the Seattle match due to a minimum nine-day quarantine restriction instituted by MLS for players returning from abroad.
However, news came that MLS would use charter flights for the returning players that would allow them to sidestep the quarantine protocol entirely. But now at least three of the players will be unavailable.