Marketa Vondrousova has tested positive for coronavirus and will not play next week's event at Ostrava, the tournament announced.
The 21-year-old from the Czech Republic would have been among a number of crowd favorites at the event, like top seed Karolina Pliskova.
"I'm disappointed, but there's nothing I can do," said Vondrousova in a statement, adding that she does "feel quite good" physically.
Sad news for Czech fans.— J&T Banka Ostrava Open 2020 (@JTBankaOpen) October 16, 2020
Marketa Vondrousova had to pull out at the last minute because her COVID-19 test came out positive.
"I'm disappointed, but there's nothing I can do. I feel quite good, so hopefully it will stay that way," said Vondroušová.
GET WELL SOON, Maky! pic.twitter.com/l7dhaC6bIo
In September, the world No. 20 and 2019 Roland Garros finalist reached the semifinals in Rome, but was ousted in the first round of Roland Garros by eventual champion Iga Swiatek.
Vondrousova's spot in the Ostrava draw has been filled by fellow Czech Barbora Strycova.
Other players who have withdrawn from the event include Petra Kvitova, Johanna Konta and Angelique Kerber—along with Sloane Stephens in qualifying—though due to injury or scheduling decisions.
The tournament also announced that Coco Gauff has been given a wildcard into qualifying.
The event is being played with no spectators.