The first group of NBA teams arrived in Orlando on Tuesday to begin the league's audacious plan to resume the 2019-20 season inside a bubble environment at Disney World. There have always been concerns about the safety of such an idea, and they've only gotten louder as coronavirus cases continue to rise in Florida. 

All along, commissioner Adam Silver has maintained faith in the league's plan and has made it clear they're moving forward, despite a number of positive tests in the past few weeks. Still, like many others, he appears to be growing more worried about the status of the pandemic. Late in June, he said his "level of concern has increased," and now he's made new comments acknowledging the possibility that a spread of the virus inside the bubble would force the league to shut down. Via ESPN:

"I think we do have the ability to trace, of course to try to understand where that positive case came from," Silver said of any positive cases inside the Walt Disney World campus. "We can actually analyze the virus itself and try to track whether if there is more than one case, if it's in essence the same virus and same genetic variation of the virus that is passed from one player to another or two people have gotten it on the campus independently. So those are all things that we are looking at."

"Certainly if we had any sort of significant spread within our campus, we would be shut down again."

At this point, it's still not clear how many cases would constitute a "significant spread," thus forcing the league to shut things down. In June, Silver told reporters that the line "hasn't been set," and we may never get a definitive number from the league, as they'll likely try to play things by ear in Orlando. 

For now, Silver and the league are trying to maintain a brave face, but the players have been more vocal about some of their issues with the whole operation. A number of players, including Victor Oladipo, Bradley Beal, Spencer Dinwiddie and Avery Bradley are all sitting out, while other players who are going have noted their hesitance. 

Last week, Portland Trail Blazers star Damian Lillard said he has little faith that players are going to follow all the rules in the bubble, and on Tuesday, Philadelphia 76ers big man Joel Embiid told reporters, "I don't think it's going to be safe enough."

Elsewhere in the sports world, MLS is dealing with a number of issues related to the virus. FC Dallas has been forced to withdraw entirely from the league's return tournament after a number of positive tests, and a game between Nashville and Chicago has been postponed for the same reason. 

While it's a completely different sport and league, the MLS situation shows why Silver and others have a growing concern that the NBA can pull off this plan and finish the season.