Czech third seed Petra Kvitova will not defend her Sydney International crown after succumbing to a gastrointestinal illness.
Tournament organisers confirmed the defending champion had to withdraw on Sunday, after she was forced to retire midway through her first-round match at the Shenzhen Open on Tuesday.
The 25-year-old two-time Wimbledon champion was due to play Sabine Lisicki in the opening round in Sydney.
"I'm really disappointed to have to withdraw from the Apia Sydney International but unfortunately I am still not feeling well," said Kvitova.
"Being defending champion, this tournament obviously means a lot to me and I've always had a wonderful time playing this event.
"I look forward to coming back in future years to play for my fantastic fans."