The pair had been on remand at the then Serco-run Mt Eden prison in May last year.
Mussard returned to his cell after breakfast to find four prisoners going through his belongings.
When they left, he found phone cards and other possessions missing and immediately pursued the men.
Two of them, who had moved on to another cell, told him to stop accusing them and Mussard spotted another playing pool with his cellmate.
While quizzing him, Te Pou grabbed the thin end of a cue and smashed him around the head with it, breaking the implement in two.
While Mussard lay bleeding and unconscious, the defendant took both pieces of the makeshift weapon, put them away and left the scene, Crown prosecutor Henry Steele said.
The victim spent the next 12 days in hospital after suffering a fractured skull, bleeding on the brain and needing 22 stitches for the gash above his right eye.
In a victim-impact statement he said he had required plastic surgery and would need ongoing surgical treatment.
"Clearly those injuries will be long lasting," Judge Anne Kiernan said.
Now back in France, Mussard was not content to let the incident pass.
He had instructed lawyer Martin Hislop with a view to pursuing legal action against Serco.
Hislop said he and Mussard were still in contact and a decision over how to proceed was still being considered.
When Te Pou was interviewed after the incident he told police he had previously been attacked by the man and it was "self defence".
Buckley told the court there was record of Te Pou suffering injuries only days earlier but he had refused to make a formal complaint to prison staff.
She said he had a "genuine determination to try and turn his life around" - a life that had been blighted by issued with alcohol, drugs and gambling.
Judge Kiernan accepted Te Pou seemed motivated to address his problems and she acknowledged his difficult past.
"The men in your family are either in prison or part of the criminal justice system. The women in the family are taking care of the children. Sadly it's not an unusual situation."
Te Pou was jailed for three years four months and will have to serve the entire sentence without parole because the attack constituted his second-strike offence under the three-strikes regime.
He had previously served time for an aggravated robbery.