MLS has postponed Sunday's match between D.C. United and Toronto FC, the league announced.
The match will be rescheduled at a later date.
News of MLS's decision came just minutes before the previously scheduled 9 a.m. ET start time.
The league said in a statement that the results of Saturday's COVID-19 testing revealed a positive test for one player and an inconclusive test for another player.
"Because of the arrival time of the clubs in Orlando, the league’s protocol called for retesting both teams this morning and to await the results of those tests prior to playing the match," MLS said in a statement. "Major League Soccer will continue to prioritize the health and safety of all participants of the MLS is Back Tournament in making these decisions."
According to ESPN's Stefano Fusaro, on Sunday morning, DC United showed up to the sports complex in which the game was set to take place. The Washington Post's Steven Goff reports that once the game was called off, United trained for a few minutes on one of the side fields. Toronto FC did not arrive at the field.
FC Dallas did not participate in the MLS is Back tournament after a high number of positive COVID-19 tests while Nashville SC was removed from the competition on Thursday after numerous positive tests.
The tournament began on July 8.