German world number seven Angelique Kerber withdrew from the Sydney International on Tuesday, adding to a lengthy list of ailing women stars ahead of next week's Australian Open.

The fourth seed, who won her first round match against Ukraine's Elina Svitolina in fierce heat over three sets on Monday, pulled out of the tournament citing a gastrointestinal illness.

Her withdrawal follows defending champion Petra Kvitova, who also had gastrointestinal problems, and second seed Agnieszka Radwanska who dropped out with a leg injury.

Kerber, who lost to Victoria Azarenka in Saturday's Brisbane International final, said she experienced problems overnight after Monday's victory.

"I'm very sorry I can't go on court today but I'm not feeling 100 percent," Kerber said.

"I started to feel unwell yesterday and today my stomach is not right. I don't want to risk my health before Melbourne."

The trio's withdrawals came after injury problems at other Australian tournaments for the world's top-ranked stars including Serena Williams (knee), Garbine Muguruza (foot) and Maria Sharapova (forearm).

Russian Ekaterina Makarova received a walkover into the Sydney quarter-finals following Kerber's withdrawal.

The Australian Open starts in Melbourne on Monday.
Source: AFP