PRETORIA (AFP) - Oscar Pistorius, serving a five-year jail sentence for killing his girlfriend, turns 28 on Saturday - his first birthday behind bars, and a world away from his former life as a jet-setting celebrity.

Like the other convicted criminals in South African jails, the double-amputee track star is unlikely to get any special treatment at Pretoria's Kgosi Mampuru prison.

"I think his privileges at the moment are still very limited because he just started," said Piet du Plessis, a Johannesburg-based lawyer representing Radovan Krejcir, a notorious Czech fugitive being held in the same prison as Pistorius.

Due to his physical disability, Pistorius is being held in the hospital ward of the prison, shielding him from the often brutal overcrowded cells, known for gang violence.

According to the department of correctional services, he is allowed five one-hour-long visits per month, and may receive cards for special occasions.

But despite experiencing a prison life relatively easy compared to that of the country's 160,000 other prisoners, Du Plessis was adamant that the athlete's birthday wouldn't be a happy one.

There is currently uncertainty over his prison term, as the state is appealing his conviction and "shockingly light" sentence.

The fallen Paralympian gold medallist, who shot and killed his girlfriend Reeva Steenkamp at his upmarket home in Pretoria on the early hours of Valentine's Day in 2013, had been accustomed to a life of luxury, beautiful women and fast cars.

His athletic achievements made him a poster boy for disability sport, attracting lucrative endorsement deals.

He said he shot the 29-year-old model four times through a locked bathroom door because he thought she was an intruder. He was found guilty of culpable homicide, escaping a harsher murder conviction.

Prosecutors are challenging Judge Thokozile Masipa's interpretation of murder.

The application for appeal is set for December 9.

Legal analysts believe the state's case will likely be successful - but that it could take months to conclude.

Until that time, it is likely the "Blade Runner" will stay in jail, contrary to his defence's assertion he will be eligible for house arrest after serving a sixth of his sentence.

"It's not fair to let someone out of prison and then to re-imprison them because their sentence changes," said criminal lawyer Martin Hood.

Still, said Hood, given Pistorius's high profile, he probably won't be mistreated in prison.

"I'm pretty sure he's comfortable."