The U.S. pole-vaulter Sam Kendricks tests positive for the coronavirus, sending Australia’s track team briefly into isolation.

TOKYO — Sam Kendricks, the reigning world champion in the men’s pole vault, was ruled out of the Tokyo Games after he tested positive for the coronavirus, U.S. Olympic officials announced on Thursday.

His positive result had immediate repercussions inside the athletes’ village. All 41 athletes and 13 officials from Australia’s track and field team returned to their rooms and briefly isolated as a precautionary measure after three of the team’s athletes reported that they had interacted with Kendricks. After all three returned negative tests, the rest of the team was allowed to return to its normal activities.

The news of Kendricks’s positive test, and the potential consequences for Australia, was a chaotic development the day before the start of the full slate of track and field competition. Kendricks, 28, who won a bronze medal at the 2016 Olympics, had been expected to contend for a medal again in Tokyo, but his sudden exit was another indication of the precarious nature of these Olympics.

Olympic organizers on Thursday reported 24 new coronavirus infections among Olympic personnel, including three athletes. Kendricks is the sixth American athlete to test positive.

The U.S. Olympic and Paralympic Committee said in a statement that Kendricks had been transferred to a hotel to be placed in isolation, and that his close contacts had been informed.

“Sam is an incredible and accomplished member of Team U.S.A. and his presence will be missed,” the statement said. “Out of respect for his privacy, we cannot provide more information at this time.”

It was unclear if Kendricks had been vaccinated. His father, Scott, who is also his coach, wrote in a since-deleted post on Instagram that Kendricks “feels fine and has no symptoms.”

Before he left for Tokyo, Kendricks had a big send-off in Oxford, Miss. He and Shelby McEwen, an Olympic high jumper who also grew up in the area, were feted with a parade, and Kendricks did a final public workout in front of an outdoor crowd.

Kendricks, a first lieutenant in the U.S. Army Reserve and a two-time world champion, famously stopped mid-run before one of his attempts at the 2016 Olympics to stand at attention when the national anthem began to play in the stadium for another athlete’s medal ceremony.

In Tokyo, he appeared poised to challenge for another spot on the podium. Mondo Duplantis, who grew up in Louisiana but competes for Sweden, is the heavy favorite to win the gold in his first Olympics.

Qualifying for the men’s pole vault is on Saturday, and the final is scheduled for Tuesday.

The three Australian athletes who had reported close contact with Kendricks will be allowed to train and compete but will be subject to strict protocols that limit their contact with others, the Australian Olympic Committee said in a statement.

“We will continue to be very thorough in our observance of the Tokyo playbooks and our own additional measures,” Ian Chesterman, the Australian team’s chef de mission, said in the statement. “We want every Australian athlete to be in a position to have their Olympic moment. We will continue to be vigilant.”