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.
Before his collapse, Sharon appeared headed to win a third term in office at the head of Kadima, a new, centrist party he formed to build on the momentum created by his seminal summer withdrawal of soldiers and settlers from the Gaza Strip.
Although Israel and the Palestinians have not managed to use the withdrawal as a springboard for the immediate revival of stalled peace talks, there had been hope that the process would resume after Palestinian elections in January and Israeli balloting in March.
It's far from clear if any of Sharon's potential successors would have the charisma, credibility and can-do spirit that helped the prime minister begin carrying out the historic task of drawing Israel's final borders.
King Abdullah of Jordan telephoned acting Israeli Prime Minister Ehud Olmert on Saturday to express "hope that the Mideast peace process would not be affected by any circumstances and developments surrounding Ariel Sharon's illness," Jordan's official Petra news agency reported.
At synagogues throughout Israel, worshippers set aside political differences and recited a "mi sheberach" for Sharon — a prayer of well wishes. Israelis called out "Ariel, son of Vera," his mother's name.
David Zvuluni, huddled with three other worshippers outside his Jerusalem synagogue, said he opposed Sharon's Gaza withdrawal, but at this moment wished him only well.
"I don't believe there's a synagogue in the country that's not praying for Sharon," he said. "There are just a few lunatics, but the rest of the people of Israel are all praying for him, even those, like us, who opposed him."
Israelis also gathered outside Hadassah on Saturday to express their solidarity.
"We are waiting for a miracle," said Eli Grossman, 51, of Kfar Saba, a Tel Aviv suburb.
"For three days I have felt I had to do this, and today, I had the chance," said Rachel Buznak, 55, who lives in Lod, outside Tel Aviv. "I really respect and admire this man. ... He didn't live for himself, just for the state."