Three Springboks have tested positive for coronavirus, forcing the cancellation of a training session scheduled for Sunday in Johannesburg, a South Africa Rugby statement said.
National director of rugby Rassie Erasmus later said the affected players were Sibusiso Nkosi, Herschel Jantjies and Vincent Koch.
All were part of the 2019 Rugby World Cup-winning squad with scrum-half Jantjies and tighthead prop Koch coming on as substitutes during the final against England in Japan.
Winger Nkosi was not part of the matchday 23 for the title decider as South Africa became world champions a record-equalling third time.
After the positive tests, the entire squad was placed in precautionary self-isolation pending specialist medical advice.
Erasmus said the squad had adhered to all the necessary protocols during training in Bloemfontein, including mandatory tests three times a week, before transferring to Johannesburg this weekend.
South Africa are preparing for home Test series against Georgia on July 2 and 9 and the British and Irish Lions on July 24, 31 and August 7, with all five matches to be staged behind closed doors.
Coronavirus has prevented the Springboks from playing since they defeated England in Yokohama on November 2, 2019.
They are also scheduled to play six Rugby Championship matches between August and October and three Tests on a November tour of Europe.
South Africa has been the hardest hit on the continent by coronavirus with 1,913,861 official cases and 59,778 deaths through June 26.