World number seven Angelique Kerber has become the latest player to be hit by injury or illness as she withdrew from the Sydney International.
The German is battling a gastrointestinal illness and withdrew from the WTA Premier event on Tuesday.
Kerber claimed a three-set win over Elina Svitolina on Monday, having come into the event on the back of being runner-up at the Brisbane International.
"I'm very sorry I can't go on court today but I'm not feeling 100 per cent. I started to feel unwell yesterday and today my stomach is not right," she said.
"I don't want to risk my health before Melbourne, of course, but I love to come back to the Apia International Sydney and always have good results here - semi-finals last year and the final two years ago.
"I hope to be feeling better soon and to play here in Sydney again in the future. I wish everyone a good week."
Kerber's withdrawal is yet another worry ahead of the Australian Open starting on Monday.
The likes of Serena Williams, Simona Halep, Garbine Muguruza, Agnieszka Radwanska, Maria Sharapova and Petra Kvitova have battled injury or illness in the lead-up to the year's first grand slam.