Boris Johnson and Rishi Sunak, the two main potential candidates in the contest to become Britain's next prime minister, will meet, the Sunday Times reported.
Johnson is a former prime minister, and Sunak a former finance minister who served under him. Neither has formally declared their candidacy.
Sunday Times Chief Political Commentator Tim Shipman said the meeting had been delayed from earlier on Saturday and may now take place on Sunday evening.
Britain's trade minister Kemi Badenoch on Saturday backed Sunak to be the next prime minister, ruling herself out of a leadership race she had considered entering.
"Rishi Sunak is the man for the job," Badenoch said in an article for the Times newspaper. Sunak has yet to formally declare his intention to run in the race, but according to a Reuters tally, has enough backers to enter.
Johnson returned to Britain on Saturday as he considers an audacious attempt to win a second term as prime minister only weeks after he was forced to step down, with some colleagues warning his comeback could create more political chaos.
Potential candidates to replace Prime Minister Liz Truss, who quit on Thursday after six weeks in office, were embarking on a frantic weekend of lobbying to secure enough nominations to enter the leadership contest before Monday's deadline.
Johnson, who was on holiday in the Caribbean when Truss resigned, has not commented publicly about a bid for his old job. He has received the support of dozens of Conservative lawmakers, but needs to secure 100 nominations to be considered.
Trade department minister James Duddridge said on Friday Johnson told him he was "up for it". He said on Saturday Johnson had secured 100 nominations, although a Reuters tally put him on about 40, while the tally showed former finance minister Rishi Sunak, for now the bookmakers' favourite, had exceeded 100.
Only former defence minister Penny Mordaunt has formally declared she will run, although a Reuters tally showed she only had 22 nominations so far before Monday's 1300 GMT deadline.
The next prime minister, a post that will have changed hands three times in four years, faces a huge inbox after Truss's economic plans hammered bond markets, raised government borrowing costs and added more strains on households and businesses already struggling with a cost-of-living crisis.
Johnson was booed by some passengers on the plane to Britain, according to a Sky News reporter on the flight which arrived in London on Saturday morning.
Wearing a dark jacket and backpack, Johnson waved to photographers at London's Gatwick Airport before driving away.
It would be a stunning comeback for the former journalist and ex-Mayor of London, who left Downing Street shrouded in scandal, saying fellow party lawmakers "changed the rules halfway through" to prevent him serving a full term.
Polarising
The prospect of another Johnson premiership is a polarising issue for many in the Conservative Party, which is deeply divided after seeing off four prime ministers in six years.
For some Conservative lawmakers, Johnson is a vote-winner, able to appeal across the country with his celebrity image and brand of energetic optimism. For others he is a toxic figure who would struggle to unite the party and so might undermine efforts to build a stable leadership to calm rattled financial markets.
Former interior minister Priti Patel said her old boss had "the mandate to deliver our elected manifesto and a proven track record getting the big decisions right."
Andrew Bridgen, another Conservative lawmaker, said he might resign from the parliamentary group if Johnson returned and told Conservatives not to create a Johnson "personality cult".
Former Conservative party leader William Hague said Johnson's return would lead to a "death spiral" for the party.
If Johnson can secure enough nominations, he could go head-to-head with Sunak, who quit as his finance minister in July, saying his former boss was unable to take tough decisions.
Johnson is currently under investigation by parliament's Privileges Committee to establish whether he lied to the House of Commons over lockdown-breaking parties. Ministers found to have knowingly misled parliament are expected to resign.
The contest has been accelerated to take only a week. Under the rules, only three candidates will be able to reach the first ballot of lawmakers on Monday afternoon, with the final two put to a vote on Friday that is limited to about 170,000 signed up members of the Conservative Party
