Attorney Gloria Allred said a previously unidentified ex-boyfriend of Bialek's will tell his version of events at a news conference in Louisiana.
Cain's wife, Gloria, meanwhile, broke her silence to defend her husband of 43 years in a television interview airing Monday night.
Bialek last week became the first woman to publicly accuse Cain, a Georgia businessman, of inappropriate sexual conduct in the late 1990s when he was chief executive of the National Restaurant Association, a Washington trade group.
Bialek had lost her job in the association's Chicago office and had gone to Washington to meet Cain for help finding employment. The two had dinner and afterward, as they sat in a parked car, Bialek said Cain groped her.
Bialek went public with her claims at a news conference last week. Allred, who accompanied Bialek, said her client had told her then-boyfriend about the incident at the time.
At least three other women have claimed that Cain sexually harassed them. Bialek is the only one of the four to go public with their accusations.
Cain has denied behaving inappropriately with anyone or knowing Bialek.
Meanwhile, Cain's wife, Gloria says her husband would have to have a "split personality" to do the things he's been accused of doing.
In the interview set to air on Fox News Channel's "On the Record," Gloria Cain said the allegations against her husband don't ring true because he "totally respects women."
"I'm thinking he would have to have a split personality to do the things that were said," she said in excerpts of the interview that were released Sunday.
She said she cannot believe the claims.
"To hear such graphic allegations and know that that would have been something that was totally disrespectful of her as a woman and I know that's not the person he is," Gloria Cain said. "He totally respects women."