Herman Cain gave cash to Ginger White
Republican candidate Herman Cain has admitted giving money to Ginger White, who says they had a 13-year affair.
In an interview with the New Hampshire Union Leader newspaper, Mr Cain also said he had not told his wife, Gloria, about the friendship.
But he insists he never had sexual relations with Ms White. He is due to hold talks with his wife on Friday.
Rival contender Newt Gingrich, who has surged in polls as Mr Cain has dropped, now predicts he will win the race.
The former House Speaker said in an interview with ABC News on Thursday: "It's very hard not to look at the recent polls and think that the odds are very high I'm going to be the nominee."
In response to Mr Gingrich's sudden rise, frontrunner Mitt Romney, a former Massachusetts governor, is preparing to launch attack ads in the key election state of Iowa on Friday.
In January, Iowa holds the first of a series of state-by-state contests that will pick the Republican nominee to challenge Barack Obama for the White House in November 2012.
Asked whether the most recent allegations of sexual misconduct to blight his campaign could force him to drop out of the race, Mr Cain told the New Hampshire newspaper: "Yes, it is an option."
He said he repeatedly gave Ms White money to help her with "month-to-month bills and expenses".
"I'm a soft-hearted person when it comes to that stuff," Mr Cain was quoted as saying. "I have helped members of my church. I have helped members of my family."
His wife of 42 years "did not know that we were friends until she [Ms White] came out with this story", he said.
Meanwhile, the Atlanta Journal-Constitution newspaper reported that it had reviewed Ms White's mobile phone records.
It found as many as 70 text messages had been exchanged between her phone and Mr Cain's between 22 October and 18 November, some in the early hours and some late at night.
Mr Cain's lawyer, Lin Wood, has asked for Ms White's phone records to "test her credibility and motive".
The former pizza executive has said he will make a decision about his campaign after a meeting with Mrs Cain on Friday.
Ms White's emergence follows allegations of sexual harassment against Mr Cain by four women, during his time as head of a restaurant lobby group in the 1990s.