Shayna Jack, who pulled back from the Australia group for the Swimming world championship, confessed to testing positive for a restricted substance on Saturday.
The 20-year-old free-form swimmer, who won two relay silvers and a bronze at the 2017 world championships, made the affirmation in an Instagram post.
"It is with great sadness and heartache that I had to leave due to allegations of having a prohibited substance in my system," she composed.
"I did NOT take this substance knowingly. Swimming has been my passion since I was 10 years old and I would never intentionally take a banned substance that would disrespect my sport and jeopardise my career.
"Now there is an ongoing investigation and my team and I are doing everything we can to find out when and how this substance has come into contact with my body."
Swimming Australia said it had been advised by the Australian Sports Anti-Doping Authority (ASADA) of an adverse test outcome following an out-of-rivalry test on June 26.
It at that point temporarily suspended Jack from the group, governing her out of contending in Gwangju, and went with her back to Australia from a preparation camp being held in Japan.
"As you would expect we are bitterly disappointed with allegations a swimmer has a prohibited substance in her system although it is important to point out that the matter is yet to be determined," said Swimming Australia CEO Leigh Russell.
The news will be a noteworthy humiliation for Australian swimming given Jack's colleague Mack Horton assumed the main job in dissents against Sun Yang at the big showdowns.
The Chinese swimmer is contending under the shadow of a World Anti-Doping Agency (WADA) bid against overseeing body FINA's choice to clear the 27-year-old of bad behavior during the irregular medication test last September.
Horton declined to join Sun on the platform after their 400 meters free-form last while Briton Duncan Scott would not shake his hand or posture for photographs with him after the 200.
Brazil's Joao de Lucca was the latest to show his displeasure at Sun's presence, refusing to shake his hand on Friday after the 4x200m freestyle relay heats.
