The incident allegedly occurred in Manhattan's York-ville ¬Endoscopy shortly before Rivers, 81, underwent a procedure on her vocal chords that led to her suffering a cardiac arrest, CNN reports.
Investigators have been informed of the incident by a member of staff at the clinic, according to the broadcaster, which also claims that gastroenterologist Dr Lawrence Cohen finished his work on the star shortly before her unidentified personal physician performed the biopsy.
However, just before performing the procedure, it is claimed that the physician took out his camera to take a picture of himself alongside Rivers, who was unconscious at the time.
During the subsequent biopsy, Rivers suddenly went into cardiac arrest, with investigators believing that her vocal chords began to swell, thereby cutting off oxygen to her lungs.
Earlier this week, a voice recording emerged of Rivers complaining of trouble with her vocal chords.
She can be heard saying: "I told [you] I didn't feel good. My voice has been bothering me. I don't know what it is (...) I feel like shit. I'm tired already."
Later, she said: "That's it - I don't feel good."