In a statement, MLS staid that one Rapids player and three staff members had tested positive, and that the Sunday's game is postponed "to allow for additional testing and evaluation."
The statement added: "All other members of the Colorado Rapids are asymptomatic, have received negative test results for COVID-19 and are following MLS medical protocol."
The postponement is the first since MLS teams began playing games in home markets following the MLS is Back tournaments, which concluded on Aug. 11.
Since then there have been less than a handful of confirmed positive tests. The Chicago Fire announced back on Aug. 21 that one of its players had a confirmed positive test.
Later on Saturday, FC Cincinnati defender Nick Hagglund revealed that he was the team's unidentified player confirmed to test positive for COVID-19 earlier this week. FCC played and lost 4-0 to New York City FC that evening.
Hagglund, 28, said he began to show symptoms on Thursday shortly after being tested for COVID-19. After that test came back as positive, Hagglund was tested again along with his wife on Friday, with the results confirming him as positive. His wife tested negative.
Information from Reuters was used in this report.