The Supreme Court of Appeal, sitting in the central city of Bloemfontein, on Monday started hearing Zuma's bid for his medical parole to be restored.
Attorney Maribolla Mphahlele, representing the prisons services, said a doctor had established that Zuma suffered "from a terminal disease or a condition that is chronic and progressive."
The doctor recommended parole due to "incapacity," as Zuma's condition had "progressively deteriorated since 2018 and (Zuma) is unable to perform the activities of daily living or self-care," Mphahlele said, without giving details.
While in prison, Zuma was taken to hospital for surgery to treat an undisclosed ailment. He did not physically appear in court on Monday.
Zuma was jailed in July for 15 months for contempt of court after he refused to give testimony to a graft inquiry.
Zuma, 80, was released on medical parole last September, just two months into a 15-month term he was handed for snubbing anti-corruption investigators.
In December, the High Court reversed his release, describing the decision as "unlawful."
His jailing sparked violent protests and looting in his home province of KwaZulu-Natal that spread to the financial hub Johannesburg in July, claiming over 350 lives and dealing a crippling blow to South Africa's economy.
It was the deadliest social unrest in South Africa since the end of white-minority rule in 1994.
Zuma ascended to the presidency in 2009 but was toppled nine years later as his tenure sank deeper into corruption scandals.
For many South Africans, his name resonates with graft and "state capture" -- the embezzlement of government-owned assets -- but he remains a hero to many grassroots members of the ruling African National Congress (ANC).
His successor, Cyril Ramaphosa, described the unrest as an orchestrated attempt to destabilize the country.
The appeal case has become a high-stakes political issue. The largest opposition party, the Democratic Alliance, describes it as "a test of the principle of equality before the law."