SYDNEY (AFP, REUTERS) - World No. 1 Ashleigh Barty announced on Tuesday (Sept 8) that she will not defend her French Open crown, citing the coronavirus fears that also prompted her to withdraw from this year's US Open.

The Australian, who claimed her maiden Grand Slam at Roland Garros in 2019, said it was a "difficult" decision but the health of her family and team came first.

"Last year's French Open was the most special tournament of my career so this is not a decision I have made lightly," she said on social media.

"There are two reasons for my decision - the first is the health risks that still exist with Covid. The second is my preparation, which has not been ideal without my coach being able to train with me due to the state border closures in Australia."

Barty announced in late July that she would sit out the US Open, currently being played in New York, but was still monitoring the situation with the French Open, which is due to start on Sept 27.

She said the decision not to attend was the latest development in "a challenging year for everyone".

"I wish the players and the French Federation all the best for a successful tournament," the 24-year-old said.

"I now look forward to a long pre-season and the summer in Australia."

Barty's withdrawal comes after organisers at Roland Garros said all players at the Grand Slam would be housed in two designated hotels "without exception" to reduce coronavirus risks.

French Open organisers also plan to welcome a limited number of spectators. Organisers had earlier said Roland Garros would allow 11,500 fans per day between three showcourts when the tournament starts in a departure from numerous professional sports events that have barred spectators amid the Covid-19 pandemic.

But this prompted concerns from Serena Williams, who avoids public places and takes a conservative approach to social distancing due to prior health concerns. The American said she hopes to speak with French Open organisers to "see how that works with the crowd and how we (players) will be protected".

"They have to make the best decision for them, and I have to do what's best for me. But I think it should be okay," said Williams, who suffered blood clots and life-threatening pulmonary embolisms while giving birth to daughter Olympia in 2017.

"There (are) a lot of factors that hopefully - hopefully -they are thinking about, and I'm sure that they are, as this is a global pandemic."

The 38-year-old American, who is on a quest for a record-equalling 24th Grand Slam title, said she misses playing in front of the legions of fans who regularly support her but has largely adapted to the unusual circumstances at the ongoing US Open in Flushing Meadows this year.

"I don't feel like I'm super different without a crowd," said third-seeded Williams. "I'm super passionate. This is my job. This is what I wake up to do. This is what I train to do 365 days of the year.

"Obviously I miss the crowd, because usually I'm training and I'm playing for the crowd. But now we have a virtual crowd."