World number two Simona Halep is the latest big name to pull out of the US Open.
Halep, a two-time grand slam champion, has opted to stay in Europe amid fears over coronavirus and becomes the sixth member of the top 10 to withdraw.
The tournament in New York gets under way at Flushing Meadows on August 31, just days after the Western & Southern Open has taken place at the same site.
Halep said on Twitter: "After weighing up all the factors involved and with the exceptional circumstances in which we are living, I have decided that I will not travel to New York to play the @usopen.
"I always said I would put my health at the heart of my decision and I therefore prefer to stay and train in Europe. I know the @usta and @WTA have worked tirelessly to put on a safe event and I wish everyone there a successful tournament."
The Romanian, who won a WTA tournament in Prague over the weekend, is opting to stay and train in Europe ahead of the clay-court swing, which commences immediately after the US Open.
Her withdrawal is another blow to tournament organisers, who have seen a raft of high-profile names pull out of the grand slam.
Barty was the first to do so, with Nadal following suit soon after as the world's top names still have concerns over travelling while infection rates of Covid-19 remain so high.
From the women's top 10, 2018 champion Naomi Osaka and Karolina Pliskova are the only non-Americans not to have pulled out, with Pliskova still considering her options.
On the men's side, world number one Novak Djokovic announced last week that he intends to play despite some earlier misgivings.
Djokovic, who has had the virus after staging an exhibition tournament without any social distancing in Serbia and Croatia, was concerned that safety protocols in the bio-secure bubble were too strong, but he has since confirmed he will travel.
Andy Murray will also play in the tournament after travelling to the United States last week.