The guard, who is believed to be in his 40s, was taken to Norfolk and Norwich University Hospital following the attack on 11 June.
The attack was revealed by an inmate who said the officer "was in a really bad way".
A Prison Service spokeswoman confirmed the incident is being investigated by police.
East of England Ambulance Service said a man was treated for a neck injury after it was called to an address on Knox Road at 17:22 BST.
The prisoner, who asked not to be named for fears of his safety, told BBC Radio Norfolk the officer was attacked by an inmate on the landing of A wing.
"If it hadn't been for the other officer protecting him he would have been killed," he added.
"The officer was in a really bad way. But since it happened nothing has changed.
"There aren't enough staff so we spend too much time in our cells.
"It's a case of inmates protecting the guards at the moment and it should be the other way around."
A Prison Service spokeswoman said it had recently announced a major overhaul of the prison system, including 2,500 extra frontline officers.
"HMP Norwich maintains appropriate and safe staffing levels on a daily basis and is actively recruiting for a number of prison officers," she added.
"We do not tolerate any violence against staff who work in our prisons. When incidents like this occur we will always work closely with the police to push for the strongest possible punishment."
The East of England Ambulance Service spokeswoman said: "We dispatched an ambulance crew and medical response car from the East Anglian Air Ambulance to assist.
"Medics were on scene within eight minutes of the call to treat a man, believed to be in his 40s, for a neck injury before being taken to Norfolk and Norwich University Hospital for further care."
A prison officer has suffered a neck injury after being attacked with a bladed weapon at Norwich Prison.