Olympic champion swimmer Cameron van der Burgh is perhaps facing his toughest opponent yet ― the coronavirus.

Van der Burgh, who won gold for South Africa in the 100 meter breaststroke in the 2012 London Olympics and silver in the 2016 Rio games, tweeted Sunday that he had contracted COVID-19 and was struggling, despite his fitness and age.

“I have been struggling with Covid-19 for 14 days today,” he wrote. “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 (least at risk demographic).”

The 31-year-old athlete complained of “serious fatigue” and an unshakeable cough. “Any physical activity like walking leaves me exhausted for hours,” he wrote.

Tony Marshall - PA Images via Getty Images Cameron van der Burgh raises his arms in victory at the 2012 Olympics.

On a positive note, van der Burgh reported that his severe fever had eased.

Van der Burgh, who retired from competition in 2018, used his situation to push for this summer’s Olympics in Tokyo to decide its status. Athletes who contract COVID-19 will suffer greatly in their conditioning leading up to the competition, he wrote.

Tony Marshall - PA Images via Getty Images South Africa's Cameron van der Burgh shows off his gold medal after winning the 100 meter breaststroke final.

Olympic organizers are facing growing pressure to delay the games, scheduled to begin in late July. The International Olympic Committee has said it will determine the Summer Games’ fate within a month.

David Davies - PA Images via Getty Images South Africa's Cameron van der Burgh churns to his gold medal in the London games.

“Please, look after yourself everyone! Health comes first - COVID-19 is no joke!” van der Burgh wrote.

1/ Some personal thoughts/observations for athletes health,The summer games & my own experience with contracting Covid19. — Cameron van der Burgh (@Cameronvdburgh) March 22, 2020

2/ I have been struggling with Covid-19 for 14 days today. 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 (least at risk demographic) — Cameron van der Burgh (@Cameronvdburgh) March 22, 2020

3/ Although the most severe symptoms(extreme fever) have eased, I am still struggling with serious fatigue and a residual cough that I can’t shake. Any physical activity like walking leaves me exhausted for hours. — Cameron van der Burgh (@Cameronvdburgh) March 22, 2020

4/ The loss in body conditioning has been immense and can only feel for the athletes that contract Covid-19 as they will suffer a great loss of current conditioning through the last training cycle. Infection closer to competition being the worst. — Cameron van der Burgh (@Cameronvdburgh) March 22, 2020

5/ Athletes will continue to train as there is no clarification re summer Games and thus are exposing themselves to unnecessary risk - and those that do contract will try rush back to training most likely enhancing/extending the damage/recovery time. — Cameron van der Burgh (@Cameronvdburgh) March 22, 2020

6/ Please, look after yourself everyone! Health comes first - COVID-19 is no joke! — Cameron van der Burgh (@Cameronvdburgh) March 22, 2020