American athlete Sam Kendricks was among the favorites to win the pole vault coming into the Tokyo Games. He had won gold at the 2017 and 2019 World Athletics Championships after earning bronze at the 2016 Olympics in Rio.

But the 28-year-old will not get his chance at the gold medal, with a positive coronavirus test on Thursday ruling him out of the competition. US Olympic and athletics officials said he has been placed in isolation and his contacts have been informed.

"Sam is an incredible and accomplished member of Team USA and his presence will be missed," the US Olympic and Paralympic Committee said in a statement. "Out of respect for his privacy, we cannot provide more information at this time."

He is the highest-profile athlete forced to withdraw from the games due to COVID-19. But the test result not only ended his Olympic dream, but also sent shock waves through the sport and put the pandemic back at center stage.

Who's been affected?

Kendricks' case was an unfriendly reminder of how fragile the Tokyo Olympics appear to be and how one case could end the competitive pursuits of many.

Due to the American's positive test, Australia's entire 54-person athletics team (41 athletes and 13 officials) was briefly placed into quarantine since three Australian athletes came into close contact with Kendricks. The Australian Olympic Committee later announced the trio had tested negative and all but those three could resume regular activities.

"Once again, abundant caution and our strict protocols continue to keep the team safe," Australian team leader Ian Chesterman said. "We want every Australian athlete to be in a position to have their Olympic moment. We will continue to be vigilant."

Kendricks wasn't the only pole vaulter forced to withdraw, either. Argentina's German Chiaraviglio also confirmed on social media that he wouldn't compete after testing positive. The two cases do not appear to be linked.

The Tokyo Games has received widespread criticism over the quarantine conditions for athletes. International Olympic Committee (IOC) Athletes' Commission chair Kirsty Coventry admitted improvement was needed.

"We have been working very closely with Tokyo 2020 and are working on improving on all of those experiences," Coventry said.

What is the coronavirus situation in Tokyo?

The withdrawals of the two pole vaulters coincide with a record-high amount of coronavirus cases in Tokyo for the third straight day. The Japanese capital reported 3,865 new cases on Thursday, up from 3,177 on Wednesday and double the numbers a week ago.

“We have never experienced the expansion of the infections of this magnitude,” Chief Cabinet Secretary Katsunobu Kato told reporters.

An Olympic spokesperson also confirmed Thursday that two people attending the Olympics from overseas have been admitted to a Tokyo hospital with COVID-19, though neither case appears to be serious.

The city has been in a state of emergency since July 12, though the Olympics went ahead despite public criticism that the Games could worsen the nation's outbreak.

But the International Olympic Committee (IOC) insisted Thursday that there was no link between the recent rise in infections and the presence of the Olympic Games.

"As far as I'm aware there's not a single case of an infection spreading to the Tokyo population from the athletes or Olympic movement," IOC spokesman Mark Adams told reporters.

"We have the most tested community probably anywhere... in the world, on top of that you have some of the toughest lockdown restrictions in the athlete's village."

Coronavirus concerns could only gain steam if more high-profile athletes are forced to withdraw and cases continue to rise. Despite efforts from organizers to keep the Games safe, it's clear they are still operating on a knife's edge.