A "significant spread" of coronavirus would cause the NBA season to be shut down for a second time, according to commissioner Adam Silver.
Since 23 June, 25 out of 351 players have tested positive for Covid-19.
"If we had any sort of a significant spread at all within our campus, we would be shut down again," Silver said.
"It would be concerning if once [the players] sit through our quarantine period, and then were to test positive, we would know that, in essence, there's a hole in our bubble."
The players who have already tested positive entered self-isolation and can return to training once they have been cleared by a physician.
Players and staff are expected to be tested three times a week and will stay in a quarantine environment for the duration of the competition, which could run until October.
"We can analyse the virus itself and try to track whether, if there's more than one case, if it's in essence the same virus, the same genetic variation of the virus that has passed from one player to another," Silver added.
Twenty two teams - 13 from the Western Conference and nine from the Eastern Conference - will travel to Orlando for training camps.
Six teams arrived on Tuesday, with eight more due to arrive on Wednesday and the final eight on Thursday.
They will contest eight games each to determine seedings for the play-offs at the resort's 5,000-seat indoor basketball facility, but without spectators.
To date 3.9 million Americans have tested positive for coronavirus.
- NBA 'bubble' to cost 150m dollars
- Black Lives Matter: NBA discusses painting courts when season resumes
How will the format work?
The Los Angeles Lakers, Los Angeles Clippers, Denver Nuggets, Utah Jazz, Oklahoma City Thunder, Houston Rockets, Dallas Mavericks and Memphis Grizzlies are in play-off positions in the Western Conference.
The Milwaukee Bucks, Toronto Raptors, Boston Celtics, Miami Heat, Indiana Pacers, Philadelphia 76ers, Brooklyn Nets and Orlando Magic currently occupy play-off spots in the Eastern Conference.
Those 16 teams will be joined by the New Orleans Pelicans, Portland Trail Blazers, Phoenix Suns, Sacramento Kings and San Antonio Spurs in the Western Conference and the Washington Wizards in the Eastern Conference.
The latest date possible for finishing the season - what would be game seven of the NBA finals - is 12 October.
- Disability and Me: Alex Brooker explores what it really means to be disabled in the UK
- Andy Murray's Greatest Hits: Olympic gold, Grand Slam glory and Davis Cup heroics