Richard Bacon is in a medically induced coma days after the broadcaster posted an image of himself in hospital.
The TV and radio presenter, 42, fell ill while travelling to Britain from the US, where he now lives, and was taken off the plane in a wheelchair.
Last week, he told his Twitter followers that he was in an A&E department on the NHS’s 70th birthday, joking: “I don’t like to miss a party.”
But now his sister Juliet has written on Instagram that the former Blue Peter presenter has been in an induced coma.
“This is my seventh day visiting my brother who’s been in an induced coma since last Thursday, just so grateful to the NHS x,” she wrote.
BBC Radio Nottingham presenter Dean Jackson, a long-time friend, told the BBC: “He’s been in that state (an induced coma) for a week.
“The treatment they’re giving him is to give him plenty of oxygen and they’re looking at reducing the sedative and bringing him round in the very near future – that might happen today.”
Bacon tweeted last week: “Thank God I got ill in Britain (actually on the way to Britain, was taken off the plane in a wheelchair).
“F* all the ideology driven politicians who’ve messed up America’s healthcare system. Viva the NHS. Happy 70th.”
According to reports, he said in tweets that his condition appeared to be pneumonia.
Celebrities including Keith Lemon and Jeremy Vine have sent their support.
Keith Lemon wrote: "Sending magical powers to Richard Bacon x"
Jeremy Vine wrote: "Thinking of my friend Richard Bacon and his family at this frightening time."
Dick and Dom wrote: "All our love and strength to Richard Bacon X."
Bacon revealed earlier this year that he had been diagnosed with attention deficit hyperactivity disorder (ADHD).