Australian Olympic officials are hopeful Cate Campbell will recover in time to swim alongside sister Bronte in the 50m freestyle in London, after a bout of gastro caused her to withdraw from the 100m event.
The Olympic relay gold medallist was a late scratching from Wednesday morning's heats as officials revealed she had fallen ill on Monday night.
Campbell has been in isolation for the past two days and Australian head coach Leigh Nugent said no other members of his team had been affected.
While Campbell was coming into the 100m race in strong form, her medal prospects are even higher in the 50m event, starting on Friday, where she is ranked sixth in the world this year.
And she will also be desperate to take part in order to fulfil a dream of competing at the Olympics alongside her 18-year-old sister.
Nugent said officials had decided skipping the 100m would give her the best opportunity to recover in time for her pet event.
"It's a pity she couldn't prove herself individually in (the 100m) but in the end you've got to cut your losses and try and redeem something out of these situations," Nugent said.
"We know she's a great racer and she's positioned pretty well for this 50.
"... Right now we've just got to preserve her and hopefully we can bring her out and she can do her thing."
Nugent said Campbell, who helped Australia's 4x100m freestyle relay team win gold on the opening night, had been suffering from vomiting, diarrhoea and stomach cramps and had been treated with an IV drip to keep her hydrated.
He said her condition was improving and doctors were hopeful she would be fit to race.
"The (doctors) can't perform miracles but they're doing everything they can," he said.
Campbell is rooming with her sister, but Bronte has not been affected.
It leaves Melanie Schlanger as Australia's sole representative in Wednesday morning's 100m freestyle heats.