A man is dead and a woman is in a serious condition after being attacked by an animal in Moyhu, south of Wangaratta, this morning.
Mr McDonald's wife, Mandi, 45, and their son rushed to provide assistance when they heard a noises.
Police said they had euthanised the deer at the scene near Wangaratta, about 250km (155 miles) north-east of Melbourne.
Mrs McDonald is now in a critical condition in hospital with life-threatening injuries.
Local resident Patrice Larkin said she knew the couple well.
"At some point in time while he was inside the enclosure, he was attacked by the deer", Victoria Police Acting Senior Sergeant Paul Purcell Paul Purcell said.
The family had kept the animal for about two years.
Police confirmed officers shot the deer a number of times for the safety of the family and the attending paramedic.
Autumn is mating, or rutting, season for many species of deer, and is a particularly risky time to be around the wild animals.
As many as a million wild deer are thought to be living in Victoria, according to a 2017 state government report.
He added that it's not unheard of for a deer to fatally attack humans in a domesticated scenario, adding: "Deers stop eating, they shed a huge percentage of their body weight".
Police say the deer was a Wapiti - a cross between a Red deer and an Elk.
The Australian Deer Association said it was rare for deer to attack people. (Nine) Paul McDonald and his wife Mandy were attacked by their pet deer at their Moyhu property.