Zion Williamson is facing a battle to prove his fitness ahead of the New Orleans Pelicans' NBA restart against the Utah Jazz.

The rookie forward left the NBA bubble to attend an "urgent family matter" before returning to Orlando last Friday.

Under coronavirus regulations, Williamson is required to quarantine for four days - provided he returns negative COVID-19 tests.

Pelicans vice president of basketball David Griffin expects the 20-year-old to be released "Tuesday afternoon-ish", but accepts there are concerns about his physical level ahead of the clash with the Jazz on July 30.

"Literally any player on our roster who went 13 days without doing any physical activity, it isn't going to be a given that we would just cut them loose in that next game," Griffin said.

"Particularly a player that generates as much torque as he does. So, we will see where he's at."

Williamson is not the only NBA player to be granted a leave of absence from the NBA's COVID-secure set-up in Florida, but Griffin is not concerned about the possibility of an increased risk of infection given the strict protocols in place.

Instead, he is more worried about the longer-term difficulties of ensuring everybody continues to toe the line.

"The league does such a good job of being hyper-cautious when they bring players back to the bubble that I don't really feel like that is where our jeopardy is," he said.

"I don't think that is where we have any real kind of opportunity to sort of pop the bubble. I think the real issue is going to be as this goes along further and further, is there more and more pull to sort of break rank and just walk off campus? That is when you're really going to see how well this is insulated."