Serena Williams Photo: IC

US Open organizers said Tuesday that the number of players willing to compete in the Grand Slam had exceeded their expectations despite several high-profile withdrawals over coronavirus fears.

Defending champion Rafael ­Nadal, top-ranked woman Ashleigh Barty and world No.2 Simona Halep are among a list of stars opting to skip the event because of concerns about COVID-19.

But Serena Williams, Novak Djokovic and Andy Murray are all still due to play when the tournament begins at Flushing Meadows in New York on August 31.

"As far as our field, in context of the times and how different the world is, I couldn't be happier. It's exceeded our expectations," United States Tennis Association (USTA) chief executive Mike Dowse said.

"At the end of the day it's our fans we are here to serve. They're going to see some unbelievable world-class tennis."

Halep, the current Wimbledon champion, dropped out on Monday, joining high-profile absentees that include reigning US Open champion Bianca Andreescu of Canada and Ukraine's fifth-ranked Elina Svitolina.

No.7 in the rankings Kiki Bertens and eighth-ranked Swiss ­Belinda Bencic will also be absent.

The depleted field provides Williams with a golden opportunity as she seeks a 24th career Grand Slam title to match Margaret Court's all-time record.

New York was one of the hardest-­hit US cities when COVID-19 first spiked in March and April, and a temporary hospital was even raised on the indoor courts at the US ­Tennis Center.

The virus has largely been brought under control in New York, even as cases have risen elsewhere in the country.

Approximately 90 percent of US Open participants have arrived in New York and are residing in two hotels as part of the competition's "bubble," with a few choosing to stay in private residences, Stacey ­Allaster, US Open Tournament ­Director, said on the conference call.

Allaster confirmed that if a player tests positive once the tournament starts, then they will be automatically withdrawn under New York state guidelines. 

Roger Federer was already ruled out of the event, which ends on September 13, as he recovers from knee surgery.