Seven-time Grand Slam champion Venus Williams has pulled out of an Australian Open warm-up tournament in New Zealand as she continues to battle a debilitating illness.

Williams is suffering from Sjogren’s syndrome, an auto-immune disease, and after playing a number of recent exhibition matches she announced yesterday she was not ready to play in the Auckland Classic, which starts on January 2.

“We are disappointed to have lost a player of her calibre,” tournament director Richard Palmer said.

“While withdrawals of this nature are part and parcel of sport, we sincerely feel for the fans who will also be disappointed by the news of Venus’s withdrawal.

“Next month’s ASB Classic field is one of the strongest in the tournament’s history with four players in the top 20, the eight seeds in the top 30 and all 24 direct entries in the top 70 in the world.

“This is still an exceptional field despite the withdrawal of Venus Williams.”

Palmer added: “Only last month she was reported saying she was looking forward to her first tournament of the year in Auckland and had heard great things about the ASB Classic. Her goal was to play a full schedule next year.”

Williams, whose ranking has slipped to 102 in the world, has described her medical condition as affecting her energy, ­causing fatigue and joint pains.

Germany’s Sabine Lisicki, the world number 15, is top seed in a field that also includes world top 20 players Peng Shuai, of China, Grand Slam winner Svetlana Kuznetsova, of Russia and Italy’s Flavia Pennetta.

With the Australian Open due to start on January 16, it is looking increasingly unlikely Williams will participate.