Major League Baseball’s coronavirus nightmare played out Monday in Philadelphia, raising questions anew about the prudence of continuing a season amid a pandemic.

In one Center City hotel, the Miami Marlins — with 11 of 33 players, plus two coaches, testing positive for COVID-19 since Friday — sat in quarantine and awaited further diagnostic results after playing three games in as many days against the Phillies at Citizens Bank Park. In another hotel, the New York Yankees awaited word about whether they will have to use the same clubhouse Tuesday night that the Marlins occupied over the weekend.

Phillies players and staff, having had their game against the Yankees postponed Monday night, went to the ballpark only to undergo saliva tests to determine if they were infected after sharing the field with the Marlins. Results are expected to be processed by an independent laboratory in New Jersey within 24 hours — or by Tuesday afternoon, according to multiple sources.

And commissioner Rob Manfred held his weekly conference call with the 30 team owners to discuss how this could have happened just five days into a 60-game season and why the Marlins were allowed to take the field Sunday when it would seem they weren’t in compliance with 113 pages of MLB protocols for safely playing baseball at a time when the virus is still spiking in many parts of the country.

“I think people anticipated this was a possibility,” said Howard Smith, the Phillies’ vice president of business affairs. “To this degree? Probably not. It’s unfortunate.”

The Phillies fumigated the visitors’ clubhouse “down to bare bones,” according to Smith, on Sunday evening. Staff members who might have come in contact with Marlins personnel were quarantined at home pending the outcome of tests.

Also, the Yankees asked that their clubhouse attendants be allowed to drive down from New York to handle the team’s equipment — assuming Tuesday night’s game isn’t postponed, too. MLB could decide to move the entire series to Yankee Stadium, where the teams are scheduled to play Wednesday and Thursday nights.

Although the Phillies are expected to have their results back by Tuesday, it’s possible they still won’t know if they were infected over the weekend. According to Paul Sax, clinical director of infectious diseases at Brigham and Women’s Hospital in Boston, it could take an average of four days after exposure to COVID-19 to test positive.

In keeping with MLB protocol, the Marlins didn’t travel Sunday night, as they normally would. Instead, they stayed put — apparently at the Rittenhouse Hotel, where owners of adjacent condominiums were informed that 13 hotel guests “who are part of a professional sports team” tested positive for COVID-19, according to an email obtained by The Inquirer — to await further test results.

The Marlins had their home opener against the Baltimore Orioles postponed and won’t play Tuesday night either.

In a statement, the Philadelphia Department of Public Health said the city was working to help the Marlins identify and notify all people who may have been exposed to infected players, who are receiving “no-touch food delivery” at the team hotel. The statement continued that the risk of spread outside the hotel and ballpark is “extremely low.”

A larger question now is how MLB will deal with a full-blown outbreak within one team that has the tentacles to potentially affect at least three others.

Speaking to reporters via Zoom, Washington Nationals manager Davey Martinez said events of the weekend in Philadelphia elevated his concern level “from an eight to about a 12.” He sat out part of last season with a heart problem and said now, “I’m scared.”

“We expected we were going to have positives at some point in time,” Manfred said on MLB Network. “I remain optimistic that the protocols are strong enough that it will allow us to play even through an outbreak like this and complete our season.”

This is the second COVID-19 outbreak to occur within proximity of Phillies personnel. Last month, six players and five staff members tested positive at the team’s spring training facility in Clearwater, Fla., despite what general manager Matt Klentak characterized as “airtight” precautions.

Word is that the Marlins might not have been as careful.

“If you looked at our dugout [over the weekend], you would’ve seen our trainers wiping down things, talking to players over and over, and [Phillies manager] Joe [Girardi] just making sure that everyone’s doing the right thing,” Smith said. “Unfortunately, you look at the other dugout, they’re not doing exactly what we’re doing.

“I was confident because you’re thinking everyone’s doing exactly what you’re doing. If they don’t, if somebody goes off the reservation for an hour, you could have a situation like this.”

The Marlins coronavirus news began Friday, when they placed catcher Jorge Alfaro on the injured list without explanation (players must give consent for teams to reveal that they have tested positive for COVID-19). Three more players were missing Sunday, including pitcher Jose Urena, who was scratched from his scheduled start roughly three hours before the game.

Marlins shortstop Miguel Rojas, the team’s representative in the Players Association, said the players came to a consensus Sunday, via a group chat over text messages, that everyone who had been cleared to play wanted to do so, even though MLB’s protocols during training camp stipulated that players who were so much as exposed to a person infected with the virus had to quarantine.

“We were somewhat aware that something was going on. We weren’t sure with who,” said Girardi, who wasn’t made aware of any consideration to postpone the game. “We sent a text out to our players and made sure that they knew what was going on. We’re constantly reminding the guys, you have to be safe. You can’t really have a lot of contact with other people because you put everybody in danger.”

To keep teams separated, MLB has prohibited players from fraternizing with opponents at the ballpark. But several Phillies players took extra precautions Sunday. Bryce Harper, for example, wore a mask while running the bases, which he didn’t do Friday night or Saturday.

MLB officials have been encouraged by the results of every-other-day testing. A 0.05% rate of positive tests among more than 10,000 samples collected in each of the last two weeks was lower than the overall 0.3% rate since testing began June 27 and seemed to indicate that everyone is taking seriously the measures for preventing the spread of the virus.

But those results occurred during training camp, when teams were based almost exclusively in their home cities. With the introduction of air travel and hotel stays, containing the virus was bound to become more difficult.

“You feel safe at the ballpark,” Marlins manager Don Mattingly said. “I feel safe with my surroundings going home. It’s a lot scarier on the road.”

And the Marlins train in Miami, a COVID-19 epicenter for the last month.

Some players — notably Los Angeles Angels star Mike Trout, widely considered the best player in baseball — expressed safety concerns during training camp. Others, such as Phillies shortstop Didi Gregorius, are playing despite underlying health conditions. Gregorius has a chronic kidney condition and is wearing a mask on the field at all times.

It’s unclear whether the Marlins’ contagion will cause more players to opt out. Thus far, only 15 major-league players have elected not to play this season. Among them, Los Angeles Dodgers pitcher David Price seemed to sum up the next few days.

“Now we REALLY get to see,” Price tweeted, “if MLB is going to put players’ health first.”

Staff writer Anna Orso contributed to this article.