Her decision means that this year's event, which starts in New York on August 31, will be without both of its 2019 champions after Nadal also said he would skip the tournament over health fears
Reigning US Open women's champion Bianca Andreescu said Thursday she will not defend her title, saying the Covid-19 pandemic has contributed to an inability to prepare for the event.
The 20-year-old Canadian, who defeated Serena Williams in last year's final, said she wants to concentrate on being at her best when she does return to competition.
Her decision means that this year's event, which starts in New York on August 31, will be without both of its 2019 champions after Rafael Nadal also said he would skip the tournament over health fears.
Those who aren't playing in the US Open on the women's side include Australia's top-ranked Ashleigh Barty, Ukraine's fifth-ranked Elina Svitolina, the Netherlands’ Kiki Bertens and sixth-ranked Andreescu.
Serena Williams, one title shy of matching the Grand Slam singles record 24 won by Margaret Court, will be at Flushing Meadows.
Andreescu defeated Williams 6-3, 7-5 in last year's US Open final.
Olga Govortsova of Belarus will take Andreescu's place in the US Open main draw.
Earlier Thursday, three-time champion and world No 1 Novak Djokovic confirmed that he will play the event despite initial reservations over the health protocols being implemented in New York.
Five-time champion Roger Federer, however, is missing as he recovers from knee surgery.