Cameron Norrie, the top-ranked British player, withdrew from Korea Open less than an hour before his quarterfinal matchup with American Jenson Brooksby.
The ATP verified the second seed’s absence due to sickness.
The 27-year-old Norrie said he had jet lag after defeating Kaichi Uchida of Japan 6-2, 6-2 in the previous round.
Before playing Croatian second seed Marin Cilic in the Tel Aviv Open quarterfinal, compatriot Liam Broady, 28, withdrew from the tournament.
Botic van de Zandschulp, the fifth seed from the Netherlands, was defeated by British number five Broady in three sets to go to his second ATP quarterfinal of his career and first since 2017.
He hasn’t yet offered a reason for leaving.
The other quarterfinal matchup on Friday is Vasek Pospisil of Canada against Serbia’s top seed Novak Djokovic.