Football legend George Best faces a critical 24 hours as he remains in intensive care with an infection.
His doctor Professor Roger Williams said that although Best was "holding", the medical team was "very worried".
"The next 24 hours is very critical for Mr Best as to whether he is going to survive this infection and all the consequences of it on his body."
The 59-year-old former Manchester United and Northern Ireland footballer is on a life-support machine.
Professor Williams said that although his condition had not worsened since Saturday, the lack of improvement was worrying.
"We would have liked to have seen him make some very definite improvement these past 24 hours, whereas he's remaining just the same."
Best had been relatively stable on Thursday in a general ward before he deteriorated early on Friday with the infection and was re-admitted to the intensive care unit.
Best's father, brother, sisters and son have been at London's Cromwell Hospital, but he remains unconscious as he is on a ventilator.
Professor Williams said: "I would imagine the situation will resolve itself naturally, that's what normally happens. It's not a case of switching off life support."
Phil Hughes, Best's agent, said the family were taking strength from the support offered by the public.
"They are bearing up," he said. "They would like to say thank you to all the well-wishers. It's a very hard time for all of us."
Professor Williams oversaw Best's liver transplant three years ago.
Plight a warning
Best's son, Calum, said after seeing his father: "I want to say that my dad is very ill at the moment but he is stable."
Best allowed the News of the World to print a photograph taken of him in hospital, as a warning about the dangers of alcohol.
He had asked for the picture to be taken before being transferred into intensive care, the paper said.
In it, Best looks gaunt with a yellow pallor due to his malfunctioning liver, with tubes attached to his bruised body.
Asked about the photo, Professor Williams said: "Well, we don't expect him to look pink and wonderful, do we?"
Mr Hughes said: "George could never beat his drink problem, but he told me 'I hope my plight can act as a warning to others'."
Best had previously shown signs of recovery after weeks of illness.
He was admitted to the hospital on 1 October suffering from flu-like infections and his health deteriorated rapidly at the beginning of November when he developed a kidney infection.
Belfast-born Best was arguably the most naturally gifted British footballer of his generation.
He made his professional debut for Manchester United in 1963, aged 17, and helped the club become the first English side to lift the European Cup in 1968.
Best was voted both English League and European Footballer of the Year that season and also won 37 international caps for Northern Ireland.