Mr Best, 59, who underwent a liver transplant in 2002, was said to have been "severely ill" but responding to treatment. The former player is being treated at the Cromwell Hospital in west London, where the transplant surgery was performed. Doctors said it was his only chance of survival after many years of heavy drinking.
His physician, Professor Roger Williams, said Best had been admitted to the hospital on Saturday after suffering flu-like symptoms, including a cough and a temperature.
He said the immuno- suppressant drugs that Mr Best has been taking since the transplant to prevent rejection of the new liver had made him more susceptible to infection.
Mr Best's condition deteriorated on Sunday night and he was moved into the hospital's intensive care unit, where he was given antibiotic therapy.
Professor Williams said he was not sure where the infection was located. He said: "With an infection, all the organs become involved, including the kidneys and liver, but they are all beginning to work properly again. People fear the worst because it is George Best, but there is no real cause for alarm.
"The infection has caused him to be severely ill but he is certainly responding to treatment and we hope to move him out of intensive care in the next 24 hours. He is serious but improving, with the emphasis on improving."
Mr Best is expected to spend at least the next week in hospital. He has been treated previously for infections by the hospital.
His son Calum spent some time with his father yesterday. He left the hospital at 3pm and returned an hour later. Asked how his father was, Calum said, "He's OK. He's stabilised," but he refused to answer any other questions.
Phil Hughes, Mr Best's agent, said he believed the problems had been caused by the drugs he had been taking for his liver, which had led to problems with his kidneys.
Mr Hughes said: "He's in and out of consciousness. He is very weak and finds it hard to speak. The doctors say he's on the mend, but he still doesn't look good to me. It's very stressful for everyone.''
Mr Best's admission to hospital is the latest development in the former footballer's turbulent recent life. In June this year, he was arrested and questioned on suspicion of sexually assaulting a 13-year-old girl; no charges were brought.
A few days earlier he was seen sporting two black eyes after what was reported to have been a fight with his girlfriend. He split from his wife, Alex, last year.
Stephen Purdew, co-owner of Forest Mere in Liphook, Hampshire, a health farm where he lived until this summer, said last night that his condition was "not unexpected". He said he and Best, whom he had known for 20 years, had not spoken since he left.
He added: "It doesn't surprise me. We decided to part company when he decided that he wouldn't stop drinking about two months ago. I told him that 99 per cent of people who have a liver transplant stop drinking but he hasn't.
"It is very sad. I love him dearly but it got to the point when he told me he would not drink again and he would go into rehabilitation but he didn't adhere to that and I said he should go. He is a sick man. I'm very upset. He is a wonderful man."Reuse content