Steven Barker, the boyfriend of Baby Peter's mother who was jailed for his part in the child's death, has been attacked in prison
The 6ft 4in lifer was punched to the floor by a fellow inmate and needed hospital treatment at HMP Wakefield.
The attacker - who has a history of prison violence - was ready to continue the assault when guards intervened, prison sources told Sky News Online.
Barker was knocked to the floor with a "single blow" and no weapons were used, the source added.
It is understood the attack was part of a planned ambush.
A prison service spokesman told Sky: "We can confirm that a prisoner at Wakefield was assaulted by another prisoner
"Thanks to the prompt and professional action of officers at the prison who intervened the situation was brought under control almost immediately.
"The prisoner who was attacked was provided treatment at the medical unit and the assailant is in the segregation unit."
Barker - who was the boyfriend of Baby Peter's mother, Tracey Connelly, 28 - was first jailed for his part in the death of 17-month old Peter Connelly in Tottenham, North London.
He was later given a life sentence for the rape of a two-year-old girl.
Baby Peter died in August 2007 after suffering 50 injuries including a broken spine.
Connelly, Barker and his brother Jason Owen, 37, were all jailed in May.