Dr. Stephen Brown was George Doodnaught's boss when the majority of the alleged incidents happened.
Doodnaught, is charged with 21 counts of sexual assault.
Twenty of the assaults are alleged to have taken place in the operating rooms in the hospital between 2006 and 2010. The other assault is alleged to have happened in a private clinic.
Doodnaught, 64, has pleaded not guilty to all charges. He worked at the hospital from 1981 until his arrest in 2010.
Brown testified Friday about hearing a complaint in 2010, directly from one of the alleged victims. It was that complaint that ultimately lead to criminal charges against Doodnaught.
Brown told the court he assured the woman he was taking it seriously and that her complaint would be dealt with by the hospital.
The prosecutor asked Brown, "Was this news to you, or were you aware of previous complaints?"
Dr. Brown told the court, "I was aware."
Two other women had shared similar complaints with Brown years earlier.
In 2007, an 85-year-old woman alleged Doodnaught forced his penis in her hand during a knee replacement operation.
A year later a 48-year-old woman alleged Doodnaught forced his genitals into her hand and mouth while she was sedated and undergoing a medical procedure.
Most of the other complainants have described similar assaults taking place in the operating room.
Brown told the court he looked into the first complaint but ultimately decided it had no merit.
He also testified that police launched an investigation of the second complaint, but he never told them that the hospital had previously looked into Doodnaught's conduct.
He testified he told the 85-year-old and her family that Doodnaught was known as a very "hands-on, touchy-feely doctor," with an "excellent reputation."
Brown also told the court that when he made those comments he knew of a third complaint against Doodnaught that had been made in 2006. But that those allegations were unsubstantiated.
By the time the hospital held a formal meeting about Doodnaught after the complaint in 2010, Brown told the court he had "forgotten" about that earliest alleged incident and only told senior hospital staff about the other two.
The trial continues.