The unsettled Defoe, who has been told by Spurs coach Juande Ramos that he is prepared to let him leave White Hart Lane, is reported to have spoken with O'Neill at Villa's Bodymoor Heath training ground on Wednesday.
O'Neill has been a long time admirer of the £10million rated England international and was linked with signing him during the summer.
A source told the Post: "Jermain has been to talk to Villa. The problem now is negotiating a fee and that may prove to be the sticking point."
O'Neill is keen to bolster his striking options with Luke Moore refusing a new contract, Marlon Harewood failing to make an impact and lingering doubts over John Carew's fitness.