Chancellor Rishi Sunak will be the next stand-in for Boris Johnson if DominicRaab succumbs to the coronavirus, Downing Street has said.
The Prime Minister's official spokesman said there was an "established orderof precedence" which would dictate which ministers would follow if Mr Raab was also incapacitated.
As First Secretary of State - effectively deputy prime minister - as well asbeing Foreign Secretary, Mr Raab was top of the list to deputise for Mr Johnson after he was hospitalised.
The spokesman said that after that, Mr Sunak was the next in line.
"There is an established order of precedence. The Prime Minister has appointed the Foreign Secretary as his First Secretary of State," the spokesman said.
"In line with the order of precedence, the Chancellor would follow from theForeign Secretary."
It would be a remarkable rise for 39-year-old Mr Sunak, who only becameChancellor in February after Sajid Javid resigned during Mr Johnson's Cabinet reshuffle.
He had previously held the post of Treasury chief secretary, Mr Javid's deputy, having been promoted to the Cabinet by Mr Johnson when he became Prime Minister last July.
Before that he had been a junior local government minister under Theresa May. He has however impressed MPs with a series of assured performances, as he set out plans for a series of massive bailouts to prevent the economy collapsing following the coronavirus outbreak.