The fate of this year's US Open will not be decided until June, but it is "highly unlikely" to be staged behind closed doors.
The US Tennis Association (USTA) has set up a medical advisory group to help them determine whether it will be safe to play the tournament.
The US Open is due to begin at Flushing Meadows in New York on 31 August.
More than 10,000 people have died from coronavirus in the city and lockdown measures have been extended to 15 May.
Nearly three quarters of a million people attended last year's US Open, and when asked if they would play without fans, USTA chief executive Mike Dowse said: "We're not taking anything off the table right now, but to be honest and open, I think that's highly unlikely.
"That's not really in the spirit of the celebration of tennis, and it also goes back to the health and wellbeing of our players and support staff that help run the tournament.
"Unless the medical experts come up with a solution that truly is foolproof and safe, we don't see that as an option."
A tournament behind closed doors still involves several thousand people. The USTA would be able to fulfil its commitment to broadcasters, but would still have to pay the players while missing out on vast revenue from ticket sales, food and drink, and merchandise.
The USTA is still aiming to run the tournament as scheduled, but has previously indicated it may explore the possibility of pushing it back into the autumn.
The French Tennis Federation has already rescheduled Roland Garros to run from 20 September to 4 October, pushing the tournament back four months from its original date of 24 May to 7 June.
While Wimbledon, due to be played between 29 June and 12 July, has been cancelled.
"In one sense we're very fortunate that we are the fourth Grand Slam to go, so time is on our side at this point," Dowse continued.
"The driving factor will be the health and wellbeing of the players, the fans and our staff. And to that, we just don't have enough information if we can run the tournament safely.
"We've set a time frame around June to make that decision, and the way we are approaching it is through a medical advisory group.
"We have five or six doctors consulting with us on a regular basis, and based on that information we will ultimately make the decision if it's safe to play the tournament or not."
The Billie Jean King National Tennis Centre, which stages the US Open every year, is currently operating as a 450-bed hospital for the people of New York.
Dowse says they are also making 25,000 meals a day for health care professionals, and for children who are missing out on school lunches.