Adam Peaty tested positive for COVID-19 at the Paris Olympics on Monday, the British Olympic Committee (BOA) said, less than 24 hours after he was narrowly pipped to the line in his men's 100-metre breaststroke final.
Peaty had been aiming to match Michael Phelps' record of winning the same swim race at three straight Olympics but he woke up on Sunday morning with a sore throat.
He lost the race by just 0.02 seconds to Italy's Nicolò Martinenghi, meaning he shared the silver medal with Team USA's Nic Fink.
The 29-year-old does not have to isolate from other athletes and does not have to test negative before competing again, but he will avoid making contact with others for the next few days.
Team GB and Peaty remain hopeful he will be able to compete in the relays later in the swimming programme.
"As in any case of illness, the situation is being managed appropriately, with all usual precautions being taken to keep the wider delegation healthy," Team GB said in a statement.
He said after Sunday's race that he wouldn't use any potential illness as an excuse, adding that he was delighted for Martinenghi.
"These are not excuses, these are just things that athletes have to go through everyday and never would I have an excuse for what is there," Peaty told reporters.
On Monday, he took to Instagram to thank his partner and coach and insisted his the second-place finish was a "blessing."
"A night full of raw emotion and sport in its true form," he wrote. "These last 14 months have been incredibly testing and I do not regret one training session or decision I made.
"I've continued to fight and find new ways to enjoy something that has broken me to the core and to end up with an Olympic silver through all of that is an absolute blessing. I'm more proud of the man and athlete I am from last night than I have been across my entire career."
He now has six Olympic medals, which includes three relay medals between Rio 2016 and Tokyo 2020.
The 29-year-old returned to racing in February after taking a mental health break and described his silver medal as a personal victory immediately after the race.
"In my heart I've won and these are happy tears because I said to myself that I would give my absolute best every single day and I have. You can't be upset about that," Peaty said.