Olympic swimming champion Cameron van der Burgh said he has been battling the coronavirus for the last two weeks.
The 31-year-old South African swimmer won gold in the 100-meter breaststroke at the 2012 London Olympics and silver in Rio four years later. He retired in 2018.
In a series of tweets Sunday, van der Burgh detailed that he had been "struggling" with COVID-19, the disease associated with the coronavirus, for 14 days.
He disclosed his diagnosis amid growing calls for the 2020 Tokyo Olympic Games to be postponed.
"By far the worst virus I have ever endured despite being a healthy individual with strong lungs (no smoking/sport), living a healthy lifestyle and being young," he tweeted, adding that he was in the least at-risk demographic.
He said that although the most severe symptoms, including extreme fever, had passed, he was still experiencing "serious fatigue and a residual cough."
Any physical activity, such as walking, leaves him exhausted for hours, he said.
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Van der Burgh said athletes will continue to train, as there is no clarification regarding the Tokyo Games, exposing themselves "to unnecessary risk." He said those who do contract the virus will try to rush back to training, "most likely enhancing/extending the damage and recovery time."
He advised people to look after themselves, concluding in his tweet thread, "Health comes first - COVID-19 is no joke!"