Expert medical witnesses said slapping the patient was "totally unacceptable" with one describing it as "assault", at a hearing into Dr Teo's conduct in Sydney on Wednesday.
The patient was left essentially in a vegetative state following the January 2019 surgery intended to extend her life expectancy by several months.
The hearing is probing two surgeries by Dr Teo over concerns including he did not adequately inform his patients of the risks involved with surgery.
Neurosurgeons Andrew Morokoff, Bryant Stokes and Paul D'Urso unanimously condemned Dr Teo slapping the patient but said his decision to undertake the surgery while controversial was not black and white.
"Regardless of the family members it's entirely unacceptable to slap a patient across the face," Professor D'Urso said.
Outside the hearing, Dr Teo told media the slap had in fact been a tap on the face as an alternative to other methods, which he described as "kinder and gentler" for the patient.
Professor Morokoff explained there were other medically accepted techniques to invoke pain in a patient to rouse them that didn't carry "insulting" social and cultural implications.
The experts told the commission the amount of normal brain tissue removed during the surgery was at the upper end of what they had seen during their careers.
All said they likely would not have performed the surgery given the risks involved but added the decision to offer a patient surgery could vary depending on the practitioner.
"If you asked 100 neurosurgeons what they would do they'd probably have different answers," Prof D'Urso said.
The experts were asked whether Dr Teo should have disclosed the amount of healthy brain tissue to be removed during the procedure.
They agreed it was common not to disclose it to a patient, but Prof Morokoff said in this instance the patient should have been made aware due to the extreme amount of normal brain tissue being removed.
"I think every brain surgeon in the country would be guilty of not declaring they take out normal brain tissue when they remove a brain tumour," Prof D'Urso said.
"You'd have nothing else to do other than have neurosurgeons in your commission if that was the line you took."
Dr Teo is famous for performing neurosurgery on cancer patients with tumours other doctors have deemed inoperable but has been accused of charging exorbitant fees and offering some patients false hope.
He told media before Wednesday's hearing he didn't regret performing brain surgeries that left the women with catastrophic injuries because he was acting in her best interests.
"I did it in their best interest, thinking it was going to help them - it didn't," he said.
Dr Teo was restrained by the NSW Medical Council in August 2021 from operating without the approval of another doctor after an investigation by the state's Health Care Complaints Commission.
"They're just trying to paint me to be some sort of money-hungry, reckless, non-compassionate doctor - I'm not. I just love my work. I love my patients," he said.
"I'm not trying to deny that complications happen. They do."
