Noah Lyles said he was "proud" to win 200m bronze after being hit by Covid-19 wrecked his bid to become the first man since Usain Bolt to complete an individual Olympic sprint double.
The American, 27, claimed the 100m title by five-thousandths of a second in a historic final on Sunday.
But just four days later he was helped off the track in a wheelchair as Botswana's Letsile Tebogo took the 200m crown, with Lyles having tested positive for the virus early on Tuesday morning.
He kept the positive test result a secret from his rivals and emerged for the final with his trademark exuberance, bouncing onto the track.
But after the race he conceded Covid "definitely affected my performance".
"I've had to take a lot of breaks," he added.
"I was coughing through the night. I'm more proud of myself than anything, coming out here to get a bronze with Covid.
"I was quite light-headed after that race. Shortness of breath, chest pain, but after a while I could catch my breath and get my wits about me. I'm a lot better now."
Lyles had been expected to run in the 4x100m and 4x400m relay races but in a later post on social media, he wrote: "I believe this will be the end of my 2024 Olympics.
"It is not the Olympics I dreamed of but it has left me with so much joy in my heart - I hope everyone enjoyed the show."
All seemed well when Lyles produced his usual theatrics as he excited the crowd before attempting to become only the 10th man to win 100m and 200m gold at a single Games.
Lyles, who won three world titles last year, began his pursuit of what would have been a potential four golds with a sensational 100m triumph. He beat Jamaica's Kishane Thompson in a dramatic photo finish to edge what has been described as the fastest 100m race in history - with the slowest of the eight finalists clocking an impressive 9.91 seconds.
But, after making only the sixth-fastest start in the 200m final, Lyles was unable to make up ground on Tebogo and spent almost the entire race in third, crossing the line behind US silver medallist Kenneth Bednarek.
It only became apparent just how much Lyles was struggling once he finished, appearing short of breath before he was helped into a wheelchair after being pictured lying flat-out on the track.
“We were trying to keep this close to the chest," said Lyles.
"The people who knew were the medical staff, my coach, my mum. We didn't want everybody going into a panic.
"I'm competitive. Why would you give [your rivals] an edge over you?"
He quarantined in a hotel close to the Olympic Village with his team, who he said "tried to get me on as much medication as we legally could to make sure my body could keep the momentum going".
"I still wanted to run, it was still possible, we just stayed away from everybody," Lyles said.
"This is by far the best day I've felt out of the last three days. Still not 100% but closer to 90 to 95%.
"That only works for one shot. I've got to settle down for a while. It's one and done, there's no holding back."
Defeat in the 200m ended Lyles' ambitious hopes of winning four gold medals in Paris, having had plans to add the 4x400m relay to the world 100m, 200m and 4x100m treble he achieved 12 months ago.
The 4x100m final takes place on Friday at 18:47 BST, with the 4x400m final held on Saturday at 20:00 BST.
Lyles earlier said "we haven't decided yet" regarding his participation in the relays and that he would have a "very honest and transparent chat with the coaches".
He added: "No matter what happens, this 4x100m team can handle everything. I've been with them in practice, I know they can come out with a win, break as many records as they put their mind to."
At the Tokyo Games three years ago, postponed from 2020 by the coronavirus pandemic, athletes had to compete in empty stadiums and maintain strict social distancing to tackle the spread of infections.
In Paris, while the virus has not disappeared, things have largely returned to normal.
Covid is now treated like other respiratory illnesses, with no strict protocols which prevent athletes from competing.
USA Track and Field (USATF) told BBC Sport that it and the United States Olympic and Paralympic Committee (USOPC) "swiftly enacted all necessary protocols to prioritise his health, the wellbeing of our team, and the safety of fellow competitors" after learning of Lyles' positive test.
"Our primary commitment is to ensure the safety of Team USA athletes while upholding their right to compete. After a thorough medical evaluation, Noah chose to compete tonight. We respect his decision and will continue to monitor his condition closely," USATF said.
"As an organisation, we are rigorously adhering to CDC [Centres for Disease Control and Prevention], USOPC, and IOC [International Olympic Committee] guidelines for respiratory illnesses to prevent the spread of illness among team members, safeguarding their health and performance."
Earlier in the Games, Great Britain's Adam Peaty tested positive for Covid-19 one day after winning 100m breaststroke silver, but returned to action in the pool five days later.
Noah Lyles ended the United States' 20-year wait for an Olympic men's 100m champion