The patient, aged in his 40s, is in a critical condition in intensive care at the Royal Adelaide Hospital.
His condition declined while he was in hotel quarantine at the Tom’s Court medi-hotel.
The man is the first person to be admitted to ICU with coronavirus in the state since May 2020.
South Australia recorded one new case of COVID-19 today – a child who returned from overseas and has been in isolation since her arrival.
The state has vaccinated close to 30,000 people since the rollout began in February.
This content first appear on 9news