NBA commissioner Adam Silver is concerned positive coronavirus tests may penetrate the Orlando bubble ahead of the league's planned return.

The 2019-20 NBA season is set to restart via a 22-team format at the Disney World complex in Orlando, Florida on July 30 after the campaign was halted due to COVID-19 in March.

However, there are concerns after Brooklyn Nets star Spencer Dinwiddie returned a second positive test for coronavirus – ruling him out of the season.

While Silver expects COVID-19 cases, he told Fortune Brainstorm Health: "We won't be surprised when they first come down to Orlando if we have some additional players test positive.

"What would be most concerning is once players enter this campus and then go through our quarantine period, then if they were to test positive or if we were to have any positive tests, we would know we would have an issue."

"We would know that there's, in essence, a hole in our bubble or that our quarantine or our campus is not working in some way," Silver added. "So that would be very concerning."

"We began testing all our teams roughly two weeks ago and as we reported we had a significant number of positive cases," he said. "I think that is more a representation of what is happening around the country."

"So on paper, and dealing with our experts, this should work. But we shall see. I'm confident based on the positive cases we are seeing from our players and the general public around the country that it will be safer on this campus than off this campus in part because we are going to be doing daily testing.

"But again, this virus has humbled many, so I am not going to express any higher level of confidence than we are following the protocols, and we hope it works as we designed it."

Silver continued: "I think we do have the ability to trace, of course to try to understand where that positive case came from.

"We can actually analyse the virus itself and try to track whether 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."

The Milwaukee Bucks led the NBA with a 53-12 record prior to the league's postponement.

July 30 will see the New Orleans Pelicans-Utah Jazz and Los Angeles Lakers-Los Angeles Clippers headline the NBA's comeback.