British number one Cameron Norrie pulled out of the Korea Open less than an hour before his quarter-final against American Jenson Brooksby.
The ATP confirmed the second seed was unable to play because of illness.
Norrie, 27, said he was suffering from jetlag after beating Japan’s Kaichi Uchida 6-2 6-2 in the previous round.
Compatriot Liam Broady, 28, withdrew from the Tel Aviv Open before his quarter-final against second seed Marin Cilic.
Broady, the British number five, beat Dutch fifth seed Botic van de Zandschulp in three sets to reach the second ATP quarter-final of his career and first since 2017.
No reason has yet been given for his withdrawal.
Meanwhile, Serbian top seed Novak Djokovic progressed to the semi-finals in Tel Aviv after defeating Canadian Vasek Pospisil 7-6 (7-5) 6-3.
He will take on Russian Roman Safiullin in the semi-final, while the other last-four tie pits Croatia’s Cilic against France’s Constant Lestienne.
“It was a great, positive win,” Djokovic said in his on-court interview. “Vasek is one of my best friends on the tour.
“We have known each other for many years. It is never easy playing someone you respect so much and like so much, but we are both professionals and wanted to win the match and you can see that.”
Norrie’s ATP Finals hopes hit
Norrie has won two titles this year and reached the top 10 for the first time.
He is eighth in the world and chasing a place at the season-ending ATP finals in Turin in November.
Norrie had earmarked the Korea Open and Japan Open, which starts on 3 October, as an opportunity to pick up points in the Race to Turin rankings. Currently 11th, he needs to finish in the top eight to qualify.
He became the third seeded player to withdraw from the Korea Open after sixth seed Borna Coric dropped out on Monday and third seed Taylor Fritz withdrew on Thursday.
Top seed Casper Ruud, of Norway, is also out after losing 6-2 3-6 6-2 to Japan’s Yoshihito Nishioka in the quarter-finals on Friday.
Rafael Nadal will move above Ruud in the world rankings as a result of the defeat, with the US Open and French Open runner-up falling from second to third.
Nishioka will play United States’ Aleksander Kovacevic in the last four, while eighth seed Brooksby will play Canada’s Denis Shapovalov in the other semi-final.
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