"When the person got home, on the phone were genital selfies of the thief," a female caller told an Australian radio station today.
The caller didn't say whether the images depicted a male or female offender.
Lord Mayor Robert Doyle, who is also chairman of Melbourne Health, said today that the "very nasty" incident wasn't a break-in and authorities believed a staff member responsible.
The locker room was accessed via swipe-entry only, with cameras positioned outside, he said.
"We do have certain information that we have now passed to the police and we are absolutely confident that we will get to the bottom of this," Mr Doyle said.
"I just feel so much for her, and it's just an awful, awful incident.
"It just beggars belief that this sort of thing can be done."
Royal Melbourne Hospital says the matter is being handled by police.
- AAP