One of the surgeons treating the prime minister says his chances of surviving his massive stroke are high.
But he has warned that the 77-year-old leader's ability to think and reason has probably been damaged.
Dr Jose Cohen told Channel2 TV: "Tomorrow is the day of truth. Tomorrow we will all know if what we did for him helped him or not.
Dr Cohen said he was "quite optimistic" about Mr Sharon's prospects for survival which he said were "very high now."
But he warned that "to say after such a severe trauma as this that there will be no cognitive problems is simply not to recognize the reality."
Dr Cohen did not appear on television.
His comments were broadcast by Channel 2 as an on-screen transcript.
They reinforced a widespread assumption that Mr Sharon will never return to power.
In the first briefing on the prime minister's condition in more than 24 hours, the Hadassah hospital director, Dr Shlomo Mor-Yosef, said a new cat scan the scan showed a "slight improvement" over a previous scan.
But he stressed that it didn't necessarily mean an improvement in Mr Sharon's overall condition.
"If I summarise the condition, it's still critical and stable," said Dr Mor-Yosef.
Sharon was admitted to the hospital on Wednesday after suffering a severe stroke.
He has since undergone surgery on two occasions to stop bleeding and relieve pressure inside his skull.