Four-time world champion Petria Thomas will have abdominal surgery next week, keeping her out of the pool until after Christmas, she announced.

Thomas, who was this week named the Australian swimming short course and butterfly swimmer of the year, has been suffering from stomach pains for the past three months.

Thomas will undergo abdominal surgery and an appendectomy in a Canberra Hospital next Wednesday with a specialist stating that there was a 70 per cent chance it was her appendix.

"I will be in hospital overnight and the doctors have said I will be out of action for a week and be able to resume serious training after Christmas," Thomas said in a statement.

Thomas won a silver medal behind Susie O'Neill in the 200 metres butterfly at the 1996 Atlanta Olympics before grabbing bronze in the same event at the Sydney Olympics as well as two silvers in relays.

After spending most of her career in the shadow of O'Neill, Thomas established herself as Australia's best female swimmer when O'Neill retired after the Sydney Games.

Thomas, who won three golds at the 2001 world championships in Japan and five gold medals at this year's Manchester Commonwealth Games, is aiming to compete at next year's world championships in Spain and the 2004 Olympics in Athens.

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