Boris Johnson is a "passionate, committed" leader who "won't enjoy being sick", according to his former Deputy London Mayor Victoria Borwick.
The Prime Minister was transferred to the intensive care unit at St Thomas' Hospital in London on Monday evening as what was said to be a "precaution" in case he needed to be put on a ventilator.
Victoria Borwick who worked as Mr Johnson's Deputy London Mayor told Good Morning Britain he wouldn't enjoy being sick because he was so "committed to the job".
Ms Borwick added that London's former mayor always took his health seriously and took regular exercise.
The deterioration in the Prime Minister's condition comes at a critical moment in the coronavirus crisis, with the epidemic expected to reach its peak in the UK in the coming days.
There was a palpable sense of shock in Westminster and beyond at the speed of his apparent decline following his admission to hospital on Sunday.
Downing Street said at the time that the move was a "precautionary step" as his symptoms of a cough and high temperature were continuing to persist after 10 days in self-isolation.
Initially he was said to have been continuing to work from his hospital bed and was receiving his ministerial red boxes.
But by 7pm on Monday, the decision was made to transfer him to intensive care so that a ventilator was close at hand if required.