Elina Svitolina and Kiki Bertens will not take part in this year's US Open due to concerns about coronavirus.
Svitolina and Bertens on Friday became the latest high-profile players to opt out of the tournament that is due to be played behind closed doors in New York from August 31.
With women's world number one Ash Barty having already decided against competing, three of the WTA Tour's top 10 players have now pulled out.
Svitolina, ranked fifth in the world, posted on Twitter: "Considering all the aspects, I have decided not to play the US Open 2020.
"I want to thank the USTA [United States Tennis Association], organisers and WTA for giving the players a chance to play and the fans a chance to watch this great event.
"I understand and respect all the efforts they are putting in to make it happen in a safe environment, but I still don't feel comfortable to travel to the US without putting my team and myself at high risk."
World number seven Bertens said the 14-day quarantine upon returning to the Netherlands from the USA would prove too much of hindrance to her preparation for the French Open, which will take place from September 27.
"After long consideration I have decided not to go to the States for Cincinnati [the Western and Southern Open, which has been moved to New York] and the US Open," Bertens posted on Instagram.
"The situation around COVID-19 is still that worrying and the health of everyone and the control over this virus is priority.
"[The Dutch] prime minister indicated yesterday that we should be quarantined for 14 days after coming back from the States. Of course, we respect this as a team and this would disturb our preparation for my beloved clay court tournaments in Rome and Paris.
"I hope the situation will soon take a positive turn and wish everyone good health."
The WTA Tour returned this week with the Palermo Open and, after skipping that event, world number two Simona Halep has arrived in the Czech Republic to play in the Prague Open next week.
Prague here we come pic.twitter.com/E2Yvied9rj— Simona Halep (@Simona_Halep) August 7, 2020
Halep previously admitted to having concerns about participating in the US Open.
Reigning men's singles champion Rafael Nadal will not take part due to worries about COVID-19, while Roger Federer will miss out after undergoing knee surgery.
Novak Djokovic is expected to make a definitive announcement on his participation this week.