Caesar is being held at the Manukau animal shelter while Auckland Council investigates the attack.
Darnell was his "usual self" yesterday morning, but struggling to talk and eat as he still has no feeling in his top lip, Minarapa said.
"The nerves in his top lip are damaged pretty badly. We are hoping he will get movement back, but it's not guaranteed."
Darnell faces recovery and rehabilitation but because he's "a really strong boy", he might be home soon, Minarapa said.
The pitbull was usually locked away when children were around, Minarapa said.
The attack occurred in the garage - which doubles as a sleepout - after Darnell jumped on a bed to play PlayStation, giving Caesar a fright.
He had just been dropped off by his mother, who was reversing out of the driveway when the dog started mauling Darnell.
Ceasar's owner and Darnell's uncle, Henare Carroll, said he was shocked the dog was so violent as he had been brought up around people. He expected Caesar would be put down.
The Herald understood the attack occurred on a Housing New Zealand (HNZ) property.
HNZ spokesman Glenn Conway said the agency was working with police to establish what happened in Saturday's attack.
"We cannot comment further until we have all the facts," he said.
A study published last August found 99,000 dog bites were recorded nationally in the decade to 2014 with more than 5800 requiring hospital treatment. More than 2500 charges were made under the Dog Control Act in the past five financial years. NZME