The Marlins' home opener against the Baltimore Orioles and the New York Yankees game at the Philadelphia Phillies, both scheduled for Monday night, have been postponed, MLB said.
Commissioner Rob Manfred didn't discuss canceling the season with the league's 30 team owners during a previously scheduled conference call, a source with knowledge of the call told CNN.
In an interview on MLB Network, Manfred said the Marlins will not play their game on Tuesday in Miami, either.
"We're doing some additional testing," Manfred said. "If the testing results are acceptable, the Marlins will resume play in Baltimore on Wednesday against the Orioles."
Eleven Marlins players and two coaches tested positive for the virus, ESPN reports. Marlins CEO Derek Jeter said the team is staying in Philadelphia, where it just played a three-game series, pending the results of a new round of testing.
"Postponing tonight's home opener was the correct decision to ensure we take a collective pause and try to properly grasp the totality of this situation," Jeter said in a statement.
The positive tests come just days after MLB began its abbreviated 60-game season -- which had been delayed from its usual April opening because of the pandemic -- and already threaten to upend the young season.
Dr. Anthony Fauci, the nation's leading infectious disease expert, told CNN he wants to remain optimistic about the season. Fauci said teams have put a lot of effort put into starting the season in a safe way, mainly by televising games without spectators.
"This is one of the things that could really put a halt in the progression of where you're going through the season," Fauci said. "Hopefully, they'll be able to continue and hopefully this is an outlier ... (and) a number of players and personnel are not infected ... So, we'll just have to see how this plays out."
The Marlins are not the first team to have players test positive and go on the injured list, but they are the first team to have an outbreak of this size.
To try to limit outbreaks, MLB is holding games without fans and has banned high-fives, fist bumps and spitting among players.
Still, the outbreak among players and staff underscores the difficulty -- if not impossibility -- of bringing large groups of people into close proximity for long periods of time when the coronavirus is so widespread in the American community.
Contact tracing of Miami's opponents shows how quickly the virus might spread through the league.
The Marlins played two exhibition games against the Atlanta Braves last week and played three games against the Philadelphia Phillies from Friday to Sunday.
The Phillies were set to host the New York Yankees on Monday. The Braves played three games against the New York Mets over the weekend in New York and are set to play the Tampa Bay Rays on Monday night. The Mets travel to Boston to play the Red Sox.
The Braves on Friday had to recall two catchers from their alternate training site after put