Professor Anthony Gordon, a critical care consultant in a top London hospital, has said it could be "months" before the Prime Minister, Boris Johnson, will be able to resume his job at full capacity.
"It can take many weeks to get back to normal full health, or even months," he warned.
Johnson is currently in intensive care but not on a ventilator; his condition is said to be stable. Meanwhile, there is public concern at the government's decision-making process in his absence.