Serbian international Zigic was recently signed by Birmingham on a four-year deal for an estimated £6million.
But Zigic's agent, Milan Calasan, said last week that Villa made a late attempt to contact the forward's representatives.
O'Neill, however, has rubbished the claims, insisting no contact was made by the club on the day that Zigic arrived at the Blues, or at any other time.
"There's not a grain of truth in the story that we've put in an offer for the player and I don't know where it's coming from," O'Neill told Villa's official website.
"I don't even know the player's agent."