LAKE BUENA VISTA, Fla. — MLS’s efforts to restart its season amid a pandemic experienced another setback Tuesday when Nashville SC’s first match was postponed because of a team outbreak, and the league said it would “continue to evaluate” the expansion squad’s participation in the troubled summer tournament.

Nashville’s problems came a day after FC Dallas was forced out of the MLS is Back Tournament because 10 players and one staff member had tested positive for the novel coronavirus.

The month-long competition is scheduled to start Wednesday night at the ESPN Wide World of Sports Complex with Orlando City playing Inter Miami, the league’s other expansion club. Nashville was supposed to play the late-night match against the Chicago Fire. No new date was announced.

Also, D.C. United’s scheduled opener Friday night was moved to 9 a.m. Sunday because its opponent, Toronto FC, was twice-delayed in traveling to Florida amid testing issues at home.

Five Nashville players have tested positive since arriving in Florida, and four others are undergoing further testing after inconclusive results, the league said.

One player from a third club, reportedly the Columbus Crew, also was positive among almost 600 players tested as of Sunday, the league said. (Several players who tested positive the past few months in their home markets have recovered.)

On Tuesday, four Vancouver players opted out of the tournament, citing the coronavirus.

“It is a little bit worrisome,” said Philadelphia Union captain Alejandro Bedoya, who in the buildup to the tournament was outspoken in his concerns about MLS resuming this summer. “You can sense some anxiety.”

Those with covid-19, the disease caused by the virus, are treated in an isolated area of the Swan and Dolphin resort, which is housing more than 1,000 players, staff and league officials.

Said Philadelphia Coach Jim Curtin, whose team is scheduled to play Nashville next week: “In the back of everyone’s head, as human beings, there is a little bit of concern. … The league has followed every safety protocol possible and made us as safe as possible. They are doing everything they can to get this tournament underway.”

On Monday, MLS Commissioner Don Garber told the Associated Press, “If there is a situation at any time that I believe that the protocols aren’t working, and the health and safety of our players is at risk, then I will make the decision to shut down the tournament."

The hotel is off-limits to the general public, a so-called bubble designed to prevent illness. It’s unclear whether the illnesses dodged detection before the teams left their home markets, were in an incubation period or were contracted in Florida, which has seen a major spike in cases over the past two weeks.

“Florida blowing up because Florida is going to Florida,” said Bedoya, who was raised in South Florida. He believes the current cases were contracted before traveling. “Once you get a transmission in the bubble,” he added, “I think that is a real cause for concern. Hopefully we don’t get to that point.”

All teams flew charters to Orlando. Spectators are not allowed to attend the tournament.

At the league hotel, security checkpoints dot the access roads and signs instruct pedestrians not to proceed onto the grounds. Buses carry players to workouts three miles away, rumbling under the Disney gondola and past exits to the theme parks, which will partially reopen this weekend.

Teams have their own areas in the hotel, including meeting rooms, but players cross paths in common areas. Everyone is required to wear a mask outside their room. MLS and Disney have declined repeated requests to detail how hotel workers are screened and tested.

MLS’s measures — extensive testing both in home markets before the teams arrived and additional testing during their stay — have not proved perfect.

“The biggest issue by far is getting teams safely into the bubble,” said a person close to the league, who was not authorized to speak about the situation. “The incubation period makes that tough. The protocol here is strong. The one thing that is clear is that training [in home markets] isn’t safe.”

On Monday, FC Dallas was forced to withdraw and Nashville’s participation was thrown into doubt. Nashville has not practiced in more than a week as players have isolated in their rooms.

Toronto and the Colorado Rapids had delayed their trips because of testing issues, but as of Monday night every team had arrived.

“In the world we are in right now, it’s only going to run so smoothly,” United Coach Ben Olsen said before the team traveled Friday. “So that has to be the expectation going into this.”

Los Angeles FC was among the last to arrive. Its star forward, 2019 league MVP Carlos Vela, opted out of the tournament because his wife is pregnant. Before traveling, the team kept a close eye on what was happening in Florida.

“Of course we are concerned,” LAFC Coach Bob Bradley said. “There are big challenges to this type of a situation in a bubble.”

Asked whether he was for or against the tournament taking place, Bradley said: “The way it was laid out, there wasn’t much to choose from. I am not sure I agree with that. … We’re excited to play games. Yes, there are concerns.”

The fear of illness is weighing on some players, Curtin said. “The mental side of the game is huge,” he said. “Players have things on their mind, for sure.”

Each team will play three first-round matches; they will count toward the standings for the regular season, which was suspended in March after two weekends. The knockout matches, culminating Aug. 11, will not count toward the standings.

MLS is hoping to resume the season without fans in home markets later this summer, with between 18 and 22 additional matches apiece, multiple people close to the league said.

The NBA will also create a bubble for its teams at Disney resorts and is slated to resume its season at the ESPN Wide World of Sports Complex later this month.