The Foreign Secretary deputised for the Prime Minister during his time in intensive care at St Thomas’ hospital in central London in April, and during his recovery afterwards.
Speaking at the virtual Conservative Party conference, Mr Raab revealed he was anxious Mr Johnson could have been one of the tens of thousands killed by the illness in the UK.
He said coronavirus had “hit us hard, taking lives on a tragic scale”.
“It nearly took the life of our Prime Minister, our friend as well as our leader,” he added.
“I get asked a lot how I felt, when I covered for him.
“Well, I really worried we might lose him, and I was worried for Carrie (Symonds), pregnant with baby Wilf.
“But I always had faith that with the outstanding NHS care he received and his fighting spirit, he’d pull through.”
After his release from hospital on Easter Sunday, Mr Johnson himself confirmed that his life had been in danger, saying in a video message that “it could have gone either way”.
He has since been on a mission to shed the pounds, expressing his belief that his excess weight led to his close brush with Covid-19.
In an interview with the Telegraph, the Prime Minister said he was now “thinner” having lost almost two stone.
“I try not to eat too much sometimes, and it’s basically about taking lots of exercise and not eating so much,” he told the paper.
“That’s my top tip. Eat less, move more, weigh less.”
He also told the BBC that reports he was preparing to step down next year was “sinister disinformation”.
Rumours swirled in the summer that the Prime Minister would not complete a full-term in office after claims from top aide Dominic Cummings’ father-in-law, Sir Humphry Wakefield, that he was struggling in the wake of his coronavirus battle.
Michael Gove, speaking at the Tory Party conference, said the Tory leader had made an “amazing recovery” from his bout of illness and described Mr Johnson as the “livest wire in the room”.
During his conference speech, Mr Raab admitted to praying that the country would be “equal” to the “greatest challenge in a generation” as he stepped in the Prime Minister’s shoes during the pandemic.
Admitting there would be “lessons to be learnt” following the Government’s handling of the crisis, he added: “I have to say, for every hurdle we faced, with every heart-rending loss, there was also a tale of courage, a moment of inspiration.”
Get news as it breaks from 1,000s of local, national and international sources -
a one-stop shop for news, sport, entertainment, business news, latest news, exclusives, celebrities, showbiz, politics and lifestyle from Newscabal UK