A source confirmed Blackmon's test result to The Associated Press. The Denver Post had first reported Blackmon's condition, saying Tuesday that three Rockies players had tested positive, which was confirmed by ESPN's Jeff Passan.
Of the three players who tested positive last week, two were asymptomatic and one showed symptoms, according to the Post.
Blackmon is a four-time All-Star slugger who hit .314 with 32 home runs and 86 RBIs last season. He turns 34 on July 1, the day players are set to begin reporting for the resumption of spring training.
Baseball commissioner Rob Manfred imposed a 60-game season Tuesday night after failed financial negotiations between owners and players. The season that has been delayed by the coronavirus pandemic will begin either July 23 or 24.
The Philadelphia Phillies have had seven players and five staff members test positive for the virus. The team has not identified any of them, and several other teams have said they also have players who have tested positive.
The Post reported that Blackmon tested positive last week after workouts at Coors Field in Denver. The newspaper said the Rockies then closed the ballpark, following MLB protocol.
Many players around the majors have been working out in recent weeks at either their home ballpark or their team's complex in Florida or Arizona. MLB closed all spring camp sites on Friday because of virus concerns.
Blackmon has been an All-Star the past three seasons. He is a career .304 hitter in nine years.
The Associated Press contributed to this report.