An ear, nose and throat specialist was present in the clinic operating room where Joan Rivers underwent a procedure last month — and where she went into cardiac arrest — even though the doctor was not authorized to practice medicine in the clinic, people briefed on the matter said on Thursday.

The E.N.T. specialist was brought into the operating room by Ms. Rivers’s gastroenterologist, the medical director of the Manhattan clinic, the people said. The specialist examined Ms. Rivers’s voice box twice, once before and once after the gastroenterologist performed an upper endoscopy, a procedure that used a tiny camera to look down her throat into her digestive system, the people said.

The people briefed declined to be identified, saying they did not want to become involved in potential litigation. They said they did not know the E.N.T. specialist’s name. But one of them said she was not authorized to work at the clinic. Under state and federal regulations, facilities like the clinic must review the credentials and qualifications of physicians and grant them privileges before permitting them to perform procedures.

The New York State Health Department is investigating Ms. Rivers’s treatment. Neither the gastroenterologist nor the E.N.T. specialist has been accused of wrongdoing.