Australia's Ian Thorpe competitive comeback only lasted one race after he withdrew from the 100m freestyle final at the Fina World Cup on Saturday.
Thorpe won three successive world titles at 400m freestyle
Thorpe, who had not competed since winning two gold medals at last year's Olympics, qualified fastest in heats but pulled out after feeling unwell.
"Ian's not been well this week and missed some training sessions," said Australia head coach Alan Thompson.
"He felt it was better that he did not swim tonight."
Thorpe, who posted a time of 47.87 seconds in Sydney, was said to be suffering with bronchitis
The 23-year-old had decided to take a year's sabbatical to recharge his batteries ahead of the Beijing Olympics in 2008 after a hugely successful career in the pool.
Thorpe had originally planned to make his comeback at next year's Commonwealth Games trials in Melbourne but brought his return forward.
His next race will be at the New South Wales state championships in December.
Elsewhere, compatriot Libby Lenton set a women's short-course world record of one minute 53.29 seconds for the 200m freestyle.
Lenton wiped 0.75 seconds off the previous mark of 1:54.04 set by Lindsay Benko of the United States at the 2002 World Championships in Moscow.