"I have a flu and have been feeling weak and sick for the last couple of days. I really have been trying my best to go on the court but I feel slow and (have had) no reactions," she said.

"I wanted to go out there for the crowd. It's an exhibition event and as well I think it was a great opportunity for me to play some matches and try to get in form before the Australian Open but sometimes you can't control it.

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"Nobody likes to be sick and and now I'm on medication and I have to rest and try to recover as fast as possible and then we will see how everything will go."

The 23-year-old said she was flying to Melbourne later today, ahead of the start of the Australian Open on January 19.

Her withdrawal from the Hong Kong event, which features teams from Russia, Europe, the Americas and Asia-Pacific, leaves her short of vital match practice at the start of the season.

She was thumped 6-2, 6-2 by Wimbledon champion Venus Williams on Thursday and her only other match was when she paired up with Michelle Larcher de Brito for a doubles clash, in which they beat Williams and Coco Vandeweghe.

Jankovic, who ended 2008 as world No 1 after a see-saw battle for the top spot, has yet to win one of the four majors.