Four months after the league was forced to suspend its season as the COVID-19 pandemic swept across North America, 25 MLS teams are in Orlando, Florida for the league's month-long "MLS is Back" competition.

Like the NBA, MLS chiefs elected to launch the league's return to competition inside a protective "bubble" at ESPN's Wide World of Sports Complex at Disney World in Orlando, Florida.

Games will take place without spectators, while players and coaches will be required to adhere to strict safety protocols designed to mitigate the risk posed by the coronavirus.

Yet a troubled build-up has highlighted the complexities of organising a sporting competition featuring multiple teams from Canada and the United States against the backdrop of a pandemic which so far has claimed more than 133,000 lives in the US alone.

On Monday, FC Dallas were abruptly withdrawn from the tournament after it emerged 10 players and a technical assistant with the team had all tested positive for coronavirus.

That development was followed by confirmation of another cluster of cases inside the Nashville SC camp since their arrival in Orlando.

Five Nashville players have tested positive for the disease while four other players face further testing. Nashville's opening game of the tournament -- scheduled for Wednesday against Chicago Fire -- has been postponed.

Meanwhile, player unease about playing in Florida -- where COVID-19 cases have exploded in recent weeks -- was reflected in the decision of Los Angeles FC star Carlos Vela to skip the event.

Mexico international Vela, the reigning league Most Valuable Player, is remaining in California to be with his pregnant wife.

MLS Commissioner Don Garber however struck a bullish tone in an interview with ESPN's SportsCenter on Monday, insisting that the league was in a "pretty good spot" despite the withdrawal of Dallas.

"We have 550 players that have already been tested and 13 of them have tested positive," Garber told ESPN. "Right now it's an extremely low percentage. The players that are there (in Orlando) are safe, they're comfortable, they're training, they're eating, they're recreating.

"They're doing the things in accordance with our protocols - they're wearing masks, they're socially distancing. They're managing their lives in a bubble."

Garber however signalled that the league would not hesitate to halt the restart if COVID-19 cases made it too dangerous to continue.

"We're going to make the right decisions as it relates to the health and safety of our players," Garber said. "And right now the protocol is working."

While the vast majority of MLS players have travelled to Orlando, there remains unease among some participants.

Columbus goalkeeper Matt Lampson has travelled despite being a cancer survivor who could be particularly at risk if infected with COVID-19.

"For everyone in the 'These are pro athletes. There is no risk. Nothing happens to them if they get the virus' camp - I am high risk," Lampson wrote on Twitter. And I know for a fact there are multiple others at #MLSisBack that are as well - including other players on their way here. This is serious."

Inter Miami midfielder Wil Trapp said learning of other players being infected with COVID-19 had been unsettling.

"It's certainly something that we've abruptly been faced with," Trapp said. "We're players who want to play, that's one part of it, but we're also human beings and this is bigger at times than sports."