Barker was also jailed for raping a girl in a separate case
The boyfriend of Baby Peter's mother has been attacked in prison.
Steven Barker, 33, is not thought to have been seriously hurt in the attack by another inmate at Wakefield Prison on Friday, a prison spokeswoman said.
Barker was jailed for 12 years for allowing or causing the death of Peter Connelly along with the boy's mother Tracey Connelly and lodger Jason Owen.
The spokeswoman said he had been treated in prison and the assailant was in the segregation unit.
Barker is also serving a life sentence, with a minimum term of 10 years, after being convicted of raping a two-year-old girl.
A prison spokeswoman said: "On the morning of 11 December, a prisoner at HMP Wakefield was assaulted by another prisoner.
"Thanks to the prompt and professional action of officers at HMP Wakefield who intervened, this situation was brought under control almost immediately.
"The prisoner who was assaulted received treatment in the prison's healthcare wing and the assailant is currently in the segregation unit."
Seventeen-month-old Peter Connelly had more than 50 injuries, including fractured ribs and a broken back, when he was found dead in a property in Tottenham, north London, in August 2007.