"While Sharon remains in critical condition, there is an increased danger to his life," Ze'ev Rotstein, the director of Sheba Medical Center at Tel Hashomer, where the 85-year-old has been in coma since 2006 after suffering a massive stroke.
"If a miracle doesn't happen, the situation is getting worse day by day," he said in a televised statement.
Rotstein said though doctors managed to stabilise some of Sharon's bodily functions, several vital organs, including his kidneys, are still in a decline.
The former General, who has been at the forefront leading troops in all major wars the Jewish state has faced since independence, has been in coma since January 4, 2006 when he suffered a major stroke while still serving as the premier.
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Sharon has shown sporadic positive responses to scans that measure brain activity during the last eight years, but has remained in a deep vegetative state since his initial hospitalisation.
He is revered by many in Israel as "Mr. Security" for his contributions in all the major wars since independence. He is reviled in equal measure in the Arab world as the "butcher of Sabra and Shatila".
While serving as defence minister in 1982, he masterminded Israel's invasion of Lebanon. During the invasion, Lebanese Christian militiamen allied to Israel massacred hundreds of Palestinians in two Beirut refugee camps - Sabra and Shatila - under Israeli control.
He was nevertheless elected prime minister 18 years later, pledging to achieve "security and true peace", and served until his second stroke.