Ian Harold King, a former Queensland first-grade cricketer, underwent emergency surgery at Canberra Hospital after another prisoner punched him in the face on Sunday morning.

King was jailed in June 2012 for 12 years for sexually abusing young boys in the 1980s and 1990s, and was under protection in the prison.

Corrections Minister Shane Rattenbury told ABC radio on Wednesday morning that King's protection should have meant some level of segregation from other prisoners, and police are investigating the circumstances under which he came to be attacked.

“There was a point at which these prisoners crossed over – they were not in the same area deliberately,” Mr Rattenbury said.

Fairfax Media understands King was attacked as he mixed with other prisoners during the distribution of medication.

“Obviously when somebody has protection, there is a level of segregation that goes on. It will vary for different detainees,” Mr Rattenbury said.

“I think we have to be clear that prisons are difficult environments. We face a constant challenge of ensuring security for all prisoners, we do have an obligation to ensure their safety as well as ensure their custody.

“If there's been a breakdown in that protection, then that's something we'll need to work on to improve the situation.

“We certainly can't say because of the nature of somebody's offence we'll turn a blind eye to some sort of what might be called 'rough justice'."

Police earlier this week said they believed a 27-year-old inmate carried out the assault and they were continuing to investigate. The spokesman said the motive for the alleged assault was yet to be determined, but initial reports indicated it was unprovoked.

It is understood that about three prison guards and a number of detainees saw the incident.

Mr Rattenbury said he did not believe any of the prison guards who witnessed the assault were stood down.

Investigators were questioning witnesses on Monday and watching security footage.

The spokesman said police expected to lay charges over the alleged assault.

During King's trial, the ACT Supreme Court heard that he had performed sex acts on his young male victims, had touched them indecently and had made them look at pornographic magazines and videos.

The 69-year-old former Queensland fast bowler claimed he abused the boys to make them better athletes and to help prepare them for manhood.

But his victims were left traumatised and unable to live normal lives.

He pleaded guilty to 25 sex charges, including sexual intercourse with a child and maintaining a sexual relationship with a young person. He will be eligible for parole in 2016.

with Noel Towell and Michael Inman