A friend of Boris Johnson who worked with him when he was mayor of London says the prime minister is a “really, really strong guy” and “far fitter than he looks”.
Will Walden, who was Mr Johnson’s director of communications at City Hall, said the prime minister would beat COVID-19.
Mr Johnson is in intensive care in hospital after his symptoms worsened on Monday.
Mr Walden said: “He will whip anybody’s backside on a tennis court, he runs regularly, he doesn’t smoke, he drinks moderately.
“So I think if anyone is in a good position both physically and mentally to fight off the disease then the prime minister is that person.”
Mr Walden said he had been in touch with Mr Johnson a few times in the last few weeks and added: “I had a brief exchange with him last week in which I was more concerned about him being in isolation and what he said back to me was, ‘Don’t worry, we’re going to beat it’.
“What he meant by that, which is typical of Boris, is we as a country will come together and beat this disease, rather than thinking about himself in regard to that – and that’s pretty typical of the man.”
Mr Walden told Sky News that Mr Johnson would be fighting to get better, but would be frustrated that he was not able to lead the national battle against COVID-19.
“He is strong, he will be concerned about the wider battle the country faces against this disease but he will also have been frustrated that he is in hospital.
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“But this is a terrible setback, his children and his extended family will be very concerned at this worrying time. However he is a strong man and will pull through.”
Asked about Foreign Secretary Dominic Raab, who has been asked to deputise for the prime minister, Mr Walden said he had always been Mr Johnson’s first choice for the role.
He added: “Dominic Rabb is surrounded by and will be supported by fantastic officials and a fantastic cabinet. He will make the right decisions.”