Tillerson, 64, has extensive experience in international negotiations, overseeing his oil company's activities in more than 50 countries.
His links to Russia could be problematic with Moscow facing renewed scrutiny in Washington. A Washington Post report late Friday said a secret CIA assessment found that Russia interfered in the US presidential election with the aim of tipping it in Trump's favor.
The president-elect, who has praised Putin and called for closer ties with Russia, dismissed the report.
Trump has already decided on Tillerson, according to NBC News, citing two unnamed sources close to the transition process. They cautioned, however, that nothing was final until Trump makes the official announcement, likely next week.
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Other media outlets, including CBS News and The Wall Street Journal, described Tillerson as the leading candidate for the job of top US diplomat.
Former UN Ambassador John Bolton will be Tillerson's deputy secretary of state "for day-to-day management of the department," NBC News added, citing one unnamed source.
Asked in an interview with Fox News -- which will air in full on Sunday -- why it makes sense to appoint a businessman as the nation's top diplomat, Trump said Tillerson is "much more than a business executive."
"I mean, he's a world-class player," the president-elect said. "He knows many of the players and he knows them well.
"He does massive deals in Russia. He does massive deals for the company, not for himself, for the company."
Trump and Tillerson met for more than two hours Saturday in Trump Tower, the New York Times reported, adding that chief strategist Stephen Bannon and son-in-law Jared Kushner told the president-elect the Exxon chief is in a "different league" from other candidates.
As speculation swirled about Tillerson, Trump attended the annual Army-Navy football grudge match in Baltimore. He pumped his fist and waved at the cheering crowd, as he and top aides watched the game from boxes shielded by bulletproof glass.
If he is officially nominated, Tillerson can expect sharp questioning during confirmation hearings in the US Senate.
Senator Bob Menendez, a Democrat and senior member of the Foreign Relations Committee, slammed the idea of Tillerson as secretary of state as "alarming and absurd."
"With Rex Tillerson as our Secretary of State, the Trump administration would be guaranteeing Russia has a willing accomplice in the president's cabinet guiding our nation's foreign policy," he said in a statement.
"The term conflict of interest doesn't even begin to describe the web of dubious business interests and bank accounts that Tillerson and his company Exxon shares with Vladimir Putin and Russian oil companies."
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On the Republican side, Senator John McCain expressed "concerns" over Tillerson's links to Putin, whom the senator called "a thug and a murderer."
"We will have hearings on that issue and other issues concerning him will be examined," McCain told CNN. "That's the time to make up your mind as to whether to vote yes or no."
Tillerson was awarded Russia's Order of Friendship by Putin following several years of Exxon projects in the country, including a deal to work with state-controlled oil company Rosneft, media reports said.
Republican Senator Lindsey Graham said he didn't know much about Tillerson, but "if you received an award from the Kremlin, [an] Order of Friendship, then we're gonna have some talkin'," Graham told the Washington Post.
"I don't want to prejudge the guy, but that's a bit unnerving."
The unpredictable Trump could still change his mind. Candidates under consideration over the past weeks include Bolton, former Republican presidential candidate Mitt Romney and former CIA director David Petraeus, among several others.
The outspoken former New York mayor Rudy Giuliani is no longer in the mix: Trump announced in a statement Friday that Giuliani had removed himself from the running.
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