Republican US presidential candidate Donald Trump has threatened to bring Gennifer Flowers, who once had an affair with former president Bill Clinton, to a debate with Hillary Clinton.

Trump made the threat after fellow businessman Mark Cuban, a vocal Trump opponent and Clinton supporter, said he would be in the front row for the debate.

"If dopey Mark Cuban of failed Benefactor fame wants to sit in the front row, perhaps I will put Gennifer Flowers right alongside of him!" Trump wrote on Twitter.

AAP

Flowers revealed an affair with Bill Clinton during his 1992 presidential campaign. He initially denied the relationship, but later admitted the sexual relationship under oath.

Flowers responded on her own Twitter account: "Hi Donald. You know I'm in your corner and will definitely be at the debate!"

Clinton and Trump are to face off in the first of three televised presidential debates on Monday evening.