The nation’s top infectious disease expert said that the Major League Baseball season may be in danger after 12 Miami Marlins players and two coaches tested positive for Covid-19 -- and that the outbreak doesn’t bode well for the start of professional football.

“I don’t believe they need to stop but we just need to follow this and see what happens with other teams on a day-by-day basis,” Anthony Fauci, director of the National Institute of Allergies and Infectious Diseases, said in an interview Tuesday with ABC.

Fauci, who last week threw out the first pitch on opening day for the Washington Nationals, commented after the newly started Major League Baseball season saw its first game cancellations due to the virus. The Marlins ditched the team’s home opener, according to ESPN, and the Philadelphia Phillies -- who played the Marlins this past weekend -- postponed their Monday game against New York Yankees.

“You just have to watch this, it could put it in danger,” Fauci said of the MLB season.

Asked if the National Football League will have to operate in a “bubble,” similar to the precautions undertaken by the National Basketball Association, Fauci said that’s possible.

The basketball league has planned to play the rest of its season by moving most of its teams to a facility at Disney World in Florida, using strict health and safety practices to limit contact with outsiders and playing without fans in the stands. That season restarts Thursday.

“It might be that they have to go in a bubble,” Fauci said of the NFL. “I think they’re conscientious enough and want to protect their players and protect their personnel that they will do the right thing.”

As Fauci’s remarks aired on television, ESPN reported that a fifth New England Patriots player had decided to opt out of playing the season. Running back Brandon Bolden joins defensive stalwart Dont’a Hightower and starting right tackle Marcus Cannon among those that have chosen to sit out the season due to concerns over the virus.

Following news of the positive tests among the Miami baseball team, San Francisco 49ers All-Pro defensive back Richard Sherman said during an interview with Pro Football Focus that he didn’t expect the NFL to shut down the season if it experienced a similar outbreak.

“I don’t see the league saying, ‘Hey, we’re going to shut down if 10 people get it, 15 people get it, 50 people get it,’” said Sherman. “I see them saying, ‘Hey, remove those people, replace them with new people and continue the game.’”

Pennsylvania’s Allegheny County, where the Pittsburgh Pirates play and where the Toronto Blue Jays were expected to play their home games this year before the state denied them permission, said it doesn’t expect to intervene in this year’s baseball season.

“The Pittsburgh Pirates and the Health Department were in regular communication before spring training and the season started,” the department said in a statement. “The Pirates provided the Health Department with a copy of the league’s return-to-play plan, which the department reviewed. The Health Department expects this communication to continue as needed during the season. The Health Department is not considering ordering MLB to stop playing at PNC Park at this time.”

This article was provided by Bloomberg News.