He was assaulted by three other inmates in the yard of Goulburn Correctional Centre on Friday.

A Corrective Services statement confirmed a "33-year-old inmate" sustained minor head injuries and was treated in hospital before returning the same day.

"Three inmates have been segregated while the investigation continues," Corrective Services said.

In 2002, Skaf was sentenced to 55 years' jail for his part in a series of gang rapes in Sydney's southwest.

In 2006, Skaf's sentence was reduced on appeal to a minimum of 32 years non-parole and a maximum of 38.

In August that year, Skaf was moved from Sydney's Long Bay after fellow inmates threatened to inject him with HIV-infected blood they were planning to take from another prisoner.

AAP

Originally published as Sydney gang rapist Bilal Skaf bashed in prison by Sydney Morning Herald