eNews Channel Africa reported on Sunday that the medical advisory board had decided not to grant permission for Derby-Lewis (77) to be released early on medical grounds.
Chief deputy commissioner of correctional services James Smalberger told ENCA that Derby-Lewis had been informed of the board's decision.
He said he could not disclose medical details about the prisoner, but said Derby-Lewis could opt to re-apply.
In September last year, Beeld reported that Derby-Lewis's wife, Gaye, applied for her husband's medical parole. Gaye said she would be applying for her husband's medical parole as he was suffering from cancer and from gangrene.
In 2011, he was also denied medical parole.
Derby-Lewis was sentenced to 25 years' in prison for his role in the killing of South African Communist Party general secretary Chris Hani in 1993.
He had arranged a firearm for hit-man Janusz Walus, who is also serving the same prison term.
Both were initially sentenced to death but this was commuted to life in prison when the death penalty was abolished. – Sapa