A third athlete at the Olympic Village in Tokyo has tested positive for COVID-19 with the Czech Republic team reporting the latest case on Monday.
Beach volleyball player Ondrej Perusic's opening game in seven days' time is now at risk after a PCR test confirmed his infection.
Perusic and his playing partner were due to begin their Olympic program on July 26 against opponents from Latvia.
Czech team leader Martin Doktor said in a statement they would ask to postpone the game until the infected player is cleared to play.
Perusic, who said he has been vaccinated, is the second member of the Czech delegation to test positive in Tokyo after a team official's case was reported on Saturday.
He is the third athlete who was staying at the village to test positive. Two South African men's soccer players had their COVID-19 cases announced on Sunday.
The players and a team video analyst who tested positive one day earlier were moved to the "isolation facility" managed by the Olympic organising committee.
Their 21 close contacts around the South Africa team now face extra scrutiny before their first game Thursday against Japan in Tokyo.
The monitoring regime includes daily testing, traveling in a dedicated vehicle, training separately from teammates not affected and being confined to their rooms for meals.
The conditions mean "although you are a close contact you are able to do the minimum that you need to do so that you can continue your preparation for the Games while you are being monitored," Pierre Ducrey, the Olympic Games operations director, said on Monday.
Earlier on Monday, before the Czech case was reported, Tokyo Olympic organisers confirmed three new COVID-19 cases, including a media worker arriving in Tokyo and Games staffer or official in the Chiba prefecture.
Both people, who were not identified, went into a 14-day quarantine, Games organisers said.
The Tokyo metropolitan authority reported 727 new COVID-19 cases on Monday, which was the 30th straight day the tally was higher than one week earlier. The count was 502 last Monday.
The games open Friday with no fans in nearly all event venues, including at the opening ceremony, amid a state of emergency in Tokyo, and a slower than hoped for vaccine rollout. Japanese authorities said Monday 21.6 per cent of the nation's 126 million population is fully vaccinated.
The total of Games-related infections is now 58 since July 1.
These resulted from 22,000 people arriving in Japan since July 1 with 4000 of those staying in the village, Ducrey said. Around 11,000 athletes are due to compete at the Tokyo Olympics through August 8.
Australian Associated Press