Croatia's Donna Vekic is treated by a trainer during a break in her fourth round match against United States' Jennifer Brady at the Australian Open tennis championship in Melbourne, Australia, Monday, Feb. 15, 2021.(AP Photo/Andy Brownbill)

Australia's Ash Barty hits a backhand return to United States' Shelby Rogers during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Feb. 15, 2021.(AP Photo/Andy Brownbill)

Czech Republic's Karolina Muchova celebrates winning a point against Belgium's Elise Mertens during their fourth round match at the Australian Open tennis championships in Melbourne, Australia, Monday, Feb. 15, 2021. (AP Photo/Hamish Blair)

Italy's Matteo Berrettini, left, receives medical treatment during a break while playing Russia's Karen Khachanov during their third round match at the Australian Open tennis championships in Melbourne, Australia, Saturday, Feb. 13, 2021. (AP Photo/Hamish Blair)

Spain's Rafael Nadal serves to Italy's Fabio Fognini during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Feb. 15, 2021.(AP Photo/Andy Brownbill)

Norway's Casper Ruud walks off the court as he retires in his fourth round match against Russia's Andrey Rublev at the Australian Open tennis championships in Melbourne, Australia, Monday, Feb. 15, 2021. (AP Photo/Hamish Blair)

Russia's Andrey Rublev hits a forehand to Norway's Casper Ruud during their fourth round match at the Australian Open tennis championships in Melbourne, Australia, Monday, Feb. 15, 2021. (AP Photo/Hamish Blair)

United States' Jennifer Brady reacts during her fourth round match against Croatia's Donna Vekic at the Australian Open tennis championship in Melbourne, Australia, Monday, Feb. 15, 2021.(AP Photo/Andy Brownbill)

Russia's Daniil Medvedev hits a backhand to United States' Mackenzie McDonald during their fourth round match at the Australian Open tennis championships in Melbourne, Australia, Monday, Feb. 15, 2021. (AP Photo/Hamish Blair)

United States' Mackenzie McDonald hits a forehand to Russia's Daniil Medvedev during their fourth round match at the Australian Open tennis championships in Melbourne, Australia, Monday, Feb. 15, 2021. (AP Photo/Hamish Blair)

United States' Jessica Pegula serves to Ukraine's Elina Svitolina during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Feb. 15,2021.(AP Photo/Andy Brownbill)

Ukraine's Elina Svitolina hits a backhand return to United States' Jessica Pegula during their fourth round match at the Australian Open tennis championship in Melbourne, Australia, Monday, Feb. 15, 2021.(AP Photo/Andy Brownbill)