Kate Stone, from Cambridge, was gored by the animal near Fort William and had to be airlifted to hospital in Glasgow.
Last night she was understood to be in intensive care at Southern General Hospital, with injuries to her neck and spine caused by the stag's antlers. Her condition was described as "serious but stable".
Reports suggested the 30-year-old keen outdoors-woman could be left paralysed.
Ms Stone was walking with a group of friends to the home of well-known Highland musician and guitar tutor Jim Hunter, 50, at Lochailort, near Fort William, west Inverness-shire, when the stag burst out of the darkness just after midnight on Monday morning.
Last night, Mr Hunter said: "The six of us were walking the few hundred yards down to my house in the darkness using two torches.
"Suddenly we heard the drumming of hooves and out of the night came this big black beast and ripped into us.
"It felled Kate before vanishing into the night. She was conscious but not speaking. We carried her into my shed which is fitted out comfortably and waited for the ambulance to arrive.
"The crew were on the scene very quickly. They stabilised Kate's condition, gave her oxygen then whipped her away to hospital.
"When the deer suddenly appeared on the scene there were shouts and screams of horror and fear but it was all over in seconds."
Ms Stone was rushed to the Belford Hospital in Fort William and then airlifted to Glasgow when the extent of her injuries became apparent.
The friends had been part of multinational group enjoying a three-day break at the local B&B run by Gary Burton, 51 and his wife Kasia, 35.
Mr Burton said he heard about the attack when one of Ms Stone's friends returned at 2.30am.
"I think what happened was that the stag panicked. It was trapped in a fenced garden having got through a gate. I don't think there was anywhere else to go and it charged out of the gate," he said. "It's bizarre and horrific."
The group were left shocked by the attack but managed to help Ms Stone and contact the emergency services, Mr Burton said.
The local community has never before experienced an attack of this nature, he added. "This is a one-in-a-million event which has shocked the whole community.
"We are at one with nature in Lochailort, and we have deer all around us.
"We are all hoping and praying that Kate pulls through."
A woman neighbour of Mr Hunter in the small group of detached houses close to the River Ailort said locals were wary of stags.
"When they see a human up fairly close they do not always run away. They stand there facing up to you, pawing the ground in a threatening manner.
"The rutting season is over so now they have harems of hinds to jealously guard against other stags."