Six of the world’s top 10 women – Ashleigh Barty, Halep, Elina Svitolina, Bianca Andreescu, Kiki Bertens and Belinda Bencic – will now not be travelling to New York. The four players in the top 10 who are expected to compete are Karolina Pliskova, Sofia Kenin, Serena Williams and Naomi Osaka.
Halep, who won her 21st WTA singles title in Prague on Sunday, says she prefers to stay in Europe.
“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 US Open,” she tweeted.
“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 US Open starts on August 29 but will now be without three of the four women's semi-finalists from last year, with Serena Williams the only one returning.
The men's draw has also been hit by withdrawals with Rafael Nadal, Roger Federer, Stan Wawrinka and Gael Monfils among those not taking part.
However, world No 1 Novak Djokovic will defend his title and former champion Andy Murray will also compete.