Reigning US Open women's singles champion Bianca Andreescu has announced that she will not defend her title at Flushing Meadows.
The 20-year-old Canadian beat Serena Williams in straight sets in last year's final, earning her maiden grand slam triumph.
However, Andreescu said the coronavirus pandemic has impacted on her ability to sufficiently prepare for the tournament and therefore has elected to stay away.
Rafael Nadal, who won the men's singles title in 2019, and women's world number one Ashleigh Barty are among several others to have already confirmed their absence from the tournament.
Andreescu wrote on social media: "After many discussions with those closest to me, I have made the difficult decision not to return to New York this year.
"I have taken this step in order to focus on my match fitness and ensure that I return ready to play at my highest level.
"The US Open victory last year has been the high point of my career thus far and I will miss not being there.
"However, I realize that the unforeseen challenges, including the Covid pandemic, have compromised my ability to prepare and compete to the degree necessary to play at my highest level.
"I want to express my appreciation to the USTA and the WTA for all of their efforts in making the event happen. I look forward to joining my competitors back on court soon."
Novak Djokovic revealed on Thursday that he would compete in New York.
The world number one, who tested positive for Covid-19 in June following the controversial Adria Tour, wrote on his website: "It was not an easy decision to make with all the obstacles and challenges on many sides, but the prospect of competing again makes me really excited.
"During my career, I have played some of my best matches at the USTA Billie Jean King National Tennis Center. I am aware that this time around it will be very different with all the protocols and safety measures that are put in place to protect players and people of NY.
"Nevertheless, I have trained hard with my team and got my body in shape so I am ready to adapt to new conditions. I've done all the check-ups to make sure I am fully recovered and I am ready to get back on court fully committed to playing my best tennis.
"I respect and appreciate everyone taking time, effort, and energy to organise these two events for the tennis players to be able to go back to their working field.
"Unfortunately for the players and the game itself, the current situation is not allowing everyone to travel and compete at the same level of risk, and I hope the situation will change soon and we will all be back to doing what we love and do best."
Djokovic will also compete in the Western & Southern Open, which is usually held in Cincinnati but will be played at Flushing Meadows from August 22-28.
The US Open gets under way at the same venue three days later. Both tournaments will be played without fans in attendance.