Corey Clark, who Fox has said was dropped from "American Idol" in 2003 for failing to reveal a past arrest, told "Primetime Live" that Abdul helped him with advice and money.
The hour-long special is set to air at 10 p.m. Wednesday, after the "American Idol" results show airs at 9 p.m. The Fox show is nearing its May 24-25 finale in which a winner will be chosen and get a record deal.
Clark earlier made allegations about Abdul in an interview with the Globe tabloid, which reported that he was shopping a tell-all book.
In a statement to ABC News on Tuesday, Fox said Clark never notified the network or "American Idol" producers of any concerns about the show despite "multiple opportunities" for contestants to do so.
"We will, of course, look into any evidence of improper conduct that we receive," Fox said, adding that the public should "carefully examine Mr. Clark's motives, given his apparent desire to exploit his prior involvement with 'American Idol' for profit and publicity."
Dancer-singer Abdul, known for her upbeat critiques of even the most hopeless contestants, has punched back at Clark and ABC. Her lawyer sent a letter to the network threatening legal action if the special airs.
"Mr. Clark is an admitted liar and opportunist who engages in unlawful activities. He is communicating lies about Paula Abdul in order to generate interest in a book deal," said an earlier statement issued on her behalf.
Clark was arrested after a scuffle with his sister and eventually pleaded no contest to a misdemeanor charge, ABC said.
According to ABC News, Clark claims that Abdul initiated the relationship, which started as a friendship but then became sexual.
The special reports Clark's allegation that Abdul "implored him not to talk about her to the media or publish his memoirs," ABC said, noting that Clark played one answering machine message for "Primetime Live." The contents of that message were not detailed in the ABC News statement.
Clark alleges his first private phone call with Abdul came after an associate of hers slipped Clark a piece of paper with her number.
"So she was like, 'You got to have better song choices, and I want to help you do that. I want to look out after you like, like, I'm your mom,'" Clark told "Primetime Live," according to an excerpt released by ABC News.
"And then she was like, "Well, more like your sister." And I was like, 'OK, cool, cool' ... And then she was like, "Well, maybe more like your special friend,"' Clark told the news show.
By Lynn Elber