An official with Jerusalem's Hadassah hospital said the process of gradually reducing Mr Sharon's level of sedation to gauge his responsiveness and to establish how much damage was sustained when he suffered a massive stroke last week.
The process is expected to take between six and eight hours, and only when he is out of the coma can the extent of brain damage be assessed.
Mr Sharon remains in a stable yet critical condition, after undergoing three long operations since he suffered the stroke.
One of the surgeons treating the leader said his chances of survival are high, however his ability to think and reason will be impaired.
"He will not continue to be prime minister, but maybe he will be able to understand and to speak," Argentina-born Dr Jose Cohen told The Jerusalem Post.
However, another doctor told AFP on the condition of anonymity that Mr Sharon runs the risk of paralysis and other difficulties that would prevent him from ruling the country.
"We are in no doubt that we will be able to revive him... but he will probably not be able to resume his duties," the source said.
Shlomo Moryussef, director of Hadassah hospital, said a weekend scan showed improvement, with swelling down and pressure in his skull normal.
"This is what we have all been waiting for since Wednesday ... to see how the prime minister's brain is functioning," he said.
The consensus remains, however that even if he survives, Mr Sharon will not be likely to return to politics.
Once Mr Sharon is awake, doctors will begin testing his responses, and will inform authorities of their assessment.
"They will inform us the moment they wake him up from the sedation and will know what systems were damaged and what the situation is," said justice ministry spokesman Jacob Galanti.
End of an era
Israelis and world leaders are already bracing for the end of the Sharon era, fearing his demise may spark fresh turmoil in a region marked by decades of conflict.
Deputy prime minister Ehud Olmert has assumed the premier’s responsibilities for the short term.
He presided over the weekly Cabinet meeting on Sunday, leaving Mr Sharon's usual seat empty, and said his prayers were with the leader.
"In the meantime, we will continue to do what Arik would want, running affairs as they should be," he said.
World leaders have given him their support as Mr Sharon's stand-in.
While Mr Sharon is hated in the Arab world, he has gained increasing respect in the West.
Just six weeks ago he formed a new political party Kadima, after leaving his former Likud party after months of tensions following the Gaza withdrawal that Mr Sharon spearheaded.
Kadima was expected to be victorious in March 28 elections, but without Mr Sharon at the helm, political analysts say it is an open race.