SYDNEY (REUTERS) - Petra Kvitova will not defend her title at this week's Sydney International tournament after the Czech withdrew due to a gastrointestinal illness, organisers said on Sunday.

The 25-year-old also pulled out of last week's Shenzhen Open in China with the illness and will be lacking match practice when the Australian Open, the year's first Grand Slam, begins in Melbourne on Jan 18.

"I'm really disappointed to have to withdraw ... but unfortunately I am still not feeling well," Kvitova, who has not played a competitive match since the Fed Cup final in November, said in a statement.

"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."