A top Toronto doctor testified Thursday that he concluded a sexual assault complaint from a female patient about one of his anesthesiologists was "a hallucination."

The woman, who is now 61 years old, filed the first complaint against Dr. George Doodnaught after undergoing knee replacement operation at North York General Hospital in February 2006.

Four years later, Doodnaught was arrested and is now on trial on 21 charges of sexually assaulting female patients while they were undergoing medical procedures.

Twenty of the assaults are alleged to have taken place at the hospital, and the other at a private clinic.

All of the assaults are alleged to have taken place between 2006 and 2010.

Doodnaught has pleaded not guilty to all charges.

On Friday, the woman who underwent the knee surgery said she complained to the hospital right after the operation.

She said while she was under anesthetic Doodnaught's "hands were caressing my breasts, they were pinching my nipples," she testified.

"And then I felt lips on my lips from the back, kissing me."

The assault is alleged to have happened while doctors were performing the knee surgery just steps away.

The Crown has alleged that Doodnaught's actions were hidden from view by what is called a "sterile screen" — a one-metre by 1.5-metre curtain that is draped across the patient.

The woman, whose name Is protected by court order, said she remembered Doodnaught asking her if she was okay.

"I remember answering yes," she told the court, fighting back tears. "I was scared he was going to do something to me if I didn't say I was all right. He might harm me."

The assaults continued throughout the operation, she told Justice David McCombs, who is hearing the case without a jury.

After the operation she said she filed a formal complaint with the hospital.

When Doodnaught was arrested four years later following a complaint from another patient, the woman told the court she was shocked to hear the hospital state at a news conference that there had been no prior complaints.

"I just felt so betrayed by the hospital," she said. "I was angry. I was mad. I didn't know what to do."

An investigation by the hospital and Toronto police following the 2010 allegation eventually led to the other charges being laid.

Dr. Derek Shilletto, who was acting chief of anesthesiology at the time of the 2006 complaint, testified Friday that he had met with the complainant and told her that her experience may have been the result of a hallucination because of the sedatives she'd been given — including the drug ketamine.

Shilletto said he also warned Doodnaught. "We live in a litigious society, and I told him he had to be careful that nothing he does could be perceived as inappropriate."

Shilletto told the court he didn't recall receiving a detailed formal letter from the complainant's niece that she had asked to be placed in Doodnaught's file.

Shilletto told the court he had investigated ketamine and its rare-but-possible side-effect in connection with the allegations.

"I thought, well, maybe it is hallucination," he told the court, "and that was my conclusion."

The trial continues.