World pole vault champion and Rio bronze medallist Sam Kendricks has tested positive for Covid-19 and will not compete at Tokyo 2020.
United States Olympic and athletics officials confirmed Kendricks' positive test, tweeting: "The health and safety of our athletes, coaches and staff is our top priority.
"In alignment with local rules and protocols he has been transferred to a hotel to be placed in isolation and is being supported by the USATF and USOPC staff."
Argentina's German Chiaraviglio, one of Kendricks' rivals, confirmed on social media that he was out of the Games as well, and was isolating in a hotel.
The immediate knock-on effect was that members of the Australian team had to isolate in their rooms as a precaution. Three of them are still self-isolating but have returned negative PCR tests.
Games procedures state that athletes who are contact-traced and have not yet competed are isolated from the rest of the squad.
They then have to be tested six hours prior to their competition and return a negative result in order to compete. The athletics programme begins on Friday, with the pole vault qualifying event on Saturday.
Kendricks won the world title in 2017 and 2019 and Olympic bronze in Rio 2016 and his battle with world record holder Mondo Duplantis of Sweden was expected to have been one of the highlights of the track and field programme.
"Sam is an incredible and accomplished member of Team USA and his presence will be missed. Out of respect for his privacy, we cannot provide more information at this time," the United States Olympic Committee tweeted.
United States Track and Field (USATF) said that Kendricks and his close contacts were immediately notified and protocols were activated to isolate him.
"We are following the guidance on next steps to ensure the safety of the remainder of our delegation, and to offer support to Sam," USATF tweeted.