Republican sources with knowledge of the situation said McCain probably will endorse his 2008 campaign rival, former Massachusetts Gov. Mitt Romney, The Hill reported Wednesday.
Asked if he might back a candidate in the GOP primary, McCain told The Hill, "Yeah, I think it would be several months later on."
McCain earlier this year said he would not make an endorsement during the primary.
Romney, once he dropped out of the party race, pitched in during McCain's 2008 presidential campaign, aides said.
"He went wherever and whenever he was asked," one person told The Hill.
Romney also backed McCain in his 2010 primary against former Rep. J.D. Hayworth, traveling to Arizona to stump for the senator.
Sources told The Hill it was unlikely McCain would back former House Speaker Newt Gingrich of Georgia, who has surged into the lead in recent national polls.
Although McCain's Republican colleagues in the Senate fret whether Gingrich is electable in a match-up against President Obama, McCain said: "I don't know if he's electable. You have to see how candidates evolve."