Boris Johnson is "mentally able to make decisions" and remains "accessible" to his government team, according to the former defence minister.
The prime minister has now spent three nights in intensive care with the coronavirus.
Doubts have been expressed as to whether the cabinet will be willing to make major decisions before Mr Johnson recovers, including when the UK lockdown could be lifted.
But with the PM's condition said to be improving, the former defence minister Tobias Ellwood indicated that he remains capable of signing off any big decisions.
Asked on Sky's Kay Burley@Breakfast who would be responsible should another significant challenge emerge, Mr Ellwood said: "The prime minister is mentally able to make decisions.
"He's accessible as well.
"What we're going through is unorthodox, we've not been here before, but I have been given assurances that the decision-making process can work in this difficult scenario."
Downing Street confirmed on Wednesday that Mr Johnson was in "good spirits" and making "steady progress".
Chancellor Rishi Sunak added that the prime minister had been sitting up in bed and "engaging positively" with medical staff.
However, his spokesman confirmed he is no longer working.
Mr Johnson has received oxygen but has not been on a ventilator.
Foreign Secretary Dominic Raab is deputising for him and has been chairing the daily meeting of the government's "war cabinet" since the prime minister was admitted to St Thomas' Hospital on Sunday.
He will also lead Thursday's meeting of the emergency COBRA committee, which includes leaders of the devolved governments in Scotland, Wales and Northern Ireland.
They will discuss how to review the UK's lockdown measures, which Mr Johnson had committed to look again after three weeks - a period which ends on Easter Monday.
The chancellor has said the review itself will be next week, when data from SAGE (the Scientific Advisory Group for Emergencies) becomes available.
The lockdown is expected be extended because doubts remain as to when the coronavirus outbreak might peak in the UK.
Wales has already committed to extending its lockdown beyond the Easter weekend, with the forecast warm weather again raising concerns people will be tempted to break social distancing rules.
Culture Secretary Oliver Dowden indicated to Sky News that the lockdown would indeed continue across the whole of the country.
"This is the moment at which we need to stick to the path that we've chosen," he told Kay Burley@Breakfast.
"We shouldn't be giving up this Easter weekend."
The latest figures on Wednesday reported another 938 deaths across the UK, taking the number of deaths in hospitals to 7,097.