Former finance chief Rishi Sunak is the favorite to become the next prime minister of the U.K. after former PM Boris Johnson bowed out of the race Sunday night.

Sunak, who was finance minister under Johnson and organized the effort to have him resign in July, is running on a policy of economic caution after PM Liz Truss' administration was snuffed out last week. Sunak's only remaining opposition is former defense minister Penny Mordaunt.

Both candidates are required to have at least 100 backers within the Tory party by Monday afternoon in order to be considered for a wider vote. If both candidates secure 100 supporters, the Party will then hold a vote and the winner will be announced Friday, according to CNBC.

Sunak outperformed Mordaunt in the September run for the prime minister spot, which Truss ultimately won.

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Truss was in power for just 44 days before resigning last week amid uproar at her economic policies, which called for expansive tax cuts. While her administration ultimately rolled back virtually all of her plans, the damage was done and U.K. markets remained in chaos.

Sunak announced his candidacy to replace Truss on Sunday, garnering widespread support after Johnson dropped out of the race.

"The United Kingdom is a great country but we face a profound economic crisis," Sunak wrote in a statement. "That's why I am standing to be leader of the Conservative Party and your next prime minister."

"There will be integrity, professionalism and accountability at every level of the government I lead and I will work day in and day out to get the job done," he said in a statement.

Sunak is believed to have the support of nearly 190 party members, while Mordaunt claims to have 90. If Mordaunt does not break the 100 threshold by Monday afternoon, Sunak will be named prime minister.