World No 1 Iga Swiatek has pulled out of the Korea Open due to fatigue, tournament organisers told reporters on Friday.
Defending champion and US Open finalist Jessica Pegula has also pulled out from the WTA 500 event in Seoul with a rib injury.
Poland's Swiatek, who won the French Open in June and took bronze in the Paris Olympics before losing to Pegula in the US Open's quarterfinals, had also withdrawn from last month's Canadian Open citing fatigue.
Former Wimbledon champion and world No 4 Elena Rybakina will also miss the Korea Open with a back injury, while US Open semifinalist Emma Navarro has pulled out due to a change of schedule.
Korea Open will take place between 16-22 September.