Dr. Yair Birenboim, director of Hadassah Hospital's Ein Kerem branch, spoke to Israel's Army Radio as doctors were performing a brain scan on the prime minister.
"There was expression of hopes and thoughts of incidents in which some people based optimism," he said. "That was definitely an expression that we think was premature."
On Saturday, one of Sharon's surgeons said the prime minister's chances of surviving his severe stroke are very high, but his ability to think and reason have been damaged.
Sharon's doctors ordered the Israeli leader to undergo another brain scan early Sunday before deciding whether to pull him out of an induced coma, hospital officials said.
The 77-year-old Israeli leader remained in critical condition, though his vital signs were stable and a brain scan Saturday showed a slight reduction in swelling.
Bringing him out of the coma is key to assessing how much brain damage he has suffered since a massive stroke last week. Hospital officials planned an announcement about Sharon's condition on Sunday afternoon.
The reports that doctor's talks had begun, by Israel Radio and the Haaretz daily, could not be immediately confirmed.
Doctors say the left side of Sharon's brain – the side that controls his speech and physical motion – is undamaged, and on the right side of his brain – the side that controls memory, personality and emotion – bleeding has stopped and the swelling has gone down, reports CBS News correspondent David Hawkins.
Dr. Jose Cohen, one of Sharon's surgeons, said he was "quite optimistic" about Sharon's prospects for survival, which he said were "very high now."
But when asked about possible cognitive impairment, Cohen replied, "To say after such a severe trauma as this that there will be no cognitive problems is simply not to recognize the reality."
Cohen's comments appeared on Channel 2 as a transcript broadcast on the screen. He did not appear himself. It was not immediately possible to contact Cohen by phone, and Sharon's other surgeon, Dr. Felix Umansky, declined to be interviewed.
The comments reinforced a widespread assumption that Sharon will never return to power. Israelis from all walks of life have lamented Sharon's likely departure from the political scene. With his larger-than life persona and warrior credentials, he was seen as the man most capable of disentangling the Israeli-Palestinian conflict.
Even if many Palestinians despised Sharon, CBS News correspondent Allen Pizzey says the prime minister represented possibly the only person
When waking Sharon out of his coma, doctors will be "looking for some sort of response," the Hadassah Hospital director, Dr. Shlomo Mor-Yosef, told journalists outside. "If there is no response, that would be bad news."
Asked whether Sharon's life could be saved, Mor-Yosef replied, "We believe it's possible."
Sharon, who experienced a mild stroke on Dec. 18, felt weak Wednesday and was being rushed by ambulance to Hadassah from his ranch in southern Israel when a blood vessel on the right side of his brain burst, causing massive cerebral hemorrhaging.
He has undergone surgery twice to stop bleeding in the brain and to relieve pressure inside his skull. Although doctors treating him have not offered a prognosis, outside experts have said the outlook is grim. Aides said they do not expect Sharon to return to the prime minister's office.