Ex-sports minister Tony Banks is due to be moved to a hospice in the US after suffering a massive stroke, a family friend says.
Tony Banks was taken ill on holiday in the US
The 62-year-old former Labour MP, who became Lord Stratford last year, collapsed on Thursday while holidaying in Florida with his wife, Sally.
Doctors warned the outlook was "bleak" and ex-Tory MP David Mellor said any recovery was an "impossible" hope.
Lord Stratford became an MP in 1983 but did not stand in last year's election.
The ex-MP for West Ham, was staying with friends on Sanibel Island, off the west coast of Florida, when he suffered the stroke. He was taken to a hospital in the town of Fort Myers.
A family friend added: "Sally's sister has flown out to be with her, but she has already been helped by the couple they were staying with, who are good friends and are being extremely supportive."
Mr Mellor, former Tory MP and close friend of the peer, told the BBC: "I think he is in an irrecoverable position where effectively the stroke has destroyed his brain.
"Tony is a strong chap and his heart continues to beat manfully, but I fear that... it is impossible to hope for any recovery, sadly."
The BBC's political editor, Nick Robinson, described the peer as "one of the great characters of Westminster" who cares passionately about politics.
'Man of the people'
Lord Stratford was known for his forthright views while an MP. His popularity with the public gave him a "man of the people" image.
His colourful language also got him into trouble at points during his Westminster career. He once described former Tory leader William Hague as a "foetus".
As an MP, his office was based in Stratford, east London, for 20 years, an area where he also lives.
He took the role of sports minister in Tony Blair's first administration, but resigned in 1999 to concentrate on the unsuccessful bid to host the 2006 World Cup at Wembley.
From the backbenches he pursued his passion for animal welfare, contributing to the Hunting Bill debate.
He is vice-president of the League Against Cruel Sports.
'Man of conviction'
He caused surprise by taking the title Lord Stratford when made a working peer last year. But he called it a "nom de politics", saying he still expected to be largely known as Tony Banks.
The current sports minister, Richard Caborn, told BBC News the peer had "left his mark in sport, football in particular", and was a "man of conviction who got his very serious point across", but was "never bitter and never personal".
Mayor of London Ken Livingstone also expressed his concern.
"This is a terrible shock and everybody's thoughts are with Tony's family at this time," he said.
Lord Pendry, a former Labour shadow minister for sport, added: "The whole of the sporting world will be hoping the worst does not happen because he was a breath of fresh air and knew more about football then any other parliamentarian. I wish him and Sally, his wife, every sympathy."