Jackson, who has been in Houston for the offseason, visited a doctor Wednesday morning because of flu-like symptoms, including chills and congestion. Jackson later received the notification of a positive test, has conferred with the Broncos' medical staff and will now isolate, in his home in Houston, for 14 days, sources said.
Jackson was the driving force behind more than 50 Broncos players, and more than 70 members of the organization overall, taking part in a peaceful Black Lives Matter march June 6 in downtown Denver.
Every player and team employee wore face coverings during the time the group was together -- everyone traveled to the event on buses, as several players spoke to the crowd in a park before the group marched downtown. Miller was also one of the players who participated.
Jackson has told team officials he believes he contracted the virus more recently, after his trip to Denver for the march. Since stay-at-home orders went into effect in mid-March, Jackson said earlier this month he had spent most of his time at his home in Houston, other than at the march.
It was unclear Wednesday evening if Jackson's diagnosis would still lead the Broncos to advise all of the players, coaches and other team employees who were at the march to be tested for the coronavirus in the coming days, though a source told ESPN's Adam Schefter that no one else has tested positive and Broncos have followed normal testing procedures. There is also the matter that quarterback Drew Lock, wide receiver Courtland Sutton and guard Dalton Risner are among a group of players that has taken part in some on-field workouts on its own in the Denver area in recent weeks.
Jackson said previously this offseason that he was trying to be as careful as possible in hopes of not contracting the coronavirus. He even went as far as the say he didn't think games should be played unless "it is completely, 100 percent safe."
Jackson was asked during a video conference call with local media early in the team's virtual offseason program what he believed it would take for the NFL to play games this fall.
"If there is any threat to us being able to contract COVID of any way and spread it to our families or anybody else that we're around, it just doesn't make sense," Jackson said.
Jackson, who signed a three-year, $33 million deal in March 2019, started 14 games last season. He was suspended for the final two games of the season for violation of the league's Policy and Program on Substances of Abuse.
The suspension stemmed from a Sept. 19 arrest and a later plea of "driving while ability impaired." He was given probation and a sentence of community service.