The Prime Minister is among those sending well wishes to Captain Sir Tom Moore, who is in hospital after testing positive for coronavirus.
The 100-year-old charity fundraiser was taken to Bedford Hospital on Sunday, after being treated for pneumonia for some time and testing positive for Covid-19 last week.
Labour leader Sir Keir Starmer also sent a get well soon message, and tweeted: “You’ve been an inspiration to us all throughout this crisis.”
The veteran’s family confirmed his illness on Sunday, with a statement on Capt Sir Tom’s Twitter page which said: “He was at home with us until today when he needed additional help with his breathing.
“He is being treated in a ward although he is not in ICU.
“We understand that everyone will be wishing him well.
“We are of course focussing on my father and will update you when we are able to.”
A spokesman for Sir Tom’s family told the BBC that he had not yet received a Covid-19 vaccine because of the medication he has been taking for pneumonia.
“Hoping for a speedy recovery and to see Captain Tom back home with his family soon,” Mr Khan added.
Michael Ball, who recorded a charity single with Capt Sir Tom that reached number one, tweeted: “Love and prayers for @captaintommoore and his lovely family as he battles this bastard of a virus.
“Stay strong Sir. We are all here for you.”
Capt Sir Tom’s fundraising efforts raised more than £32 million for the NHS, walking 100 laps of his garden before his 100th birthday during the first national lockdown in April.
The veteran set out to raise £1,000 from his lockdown charity challenge but his efforts struck a chord with the nation, and praise and donations flooded in.
In acknowledgement of his efforts, he was knighted by the Queen during a unique open-air ceremony at Windsor Castle in summer 2020.