However, both men are reportedly becoming resigned to the prospect of having to wait until the end of the season to make an offer for the England forward.
Wigan manager Steve Bruce is adamant that the striker will not be allowed to leave this month and is said to be "very confident" of holding on to his services until the end of the season.
And, according to Wigan's chief executive Brenda Spencer, Heskey has already assured the club that he intends to see out his current contract.
There was some concern at Wigan coming into this month's transfer window that, were either Villa or Liverpool to offer the club a significant amount, chairman Dave Whelan would have no option but to accept, with cashing in on Heskey now, rather than losing him to a free transfer in the summer, the lesser of two evils.
However, Heskey is also believed to prefer a wait until the summer before he leaves the club, when he will have complete control over his destination and greater financial rewards from any transfer.
It suits Wigan, who are currently looking to consolidate their position in the Premier League top 10, but it is unlikely to meet either Villa or Liverpool's requirements.
Just as Benitez is desperate to bring in a new player to offset Robbie Keane's slow transition at Anfield, O'Neill is hoping to bolster his attacking line in response to a back injury to John Carew, and the insufficient progress made by reserve striker Marlon Harewood.
Although Carew has returned to light training, his condition is insufficient to support O'Neill's aims of securing Champions League qualification.
The Villa manager has made no attempts to play down the importance of reinforcing his squad for the second half of the season, but he also accepts that reaching agreements at this stage in the year tend to be complicated.
Moreover, O'Neill has said he would be willing to pay over the odds if it meant securing a top target, and his chairman Randy Lerner would surely support him.
Whether that would stretch to the "outrageous" offer that Bruce would demand is another matter.
Wigan, meanwhile, have added Egyptian striker Mido to their squad on a loan deal, seen by some as insurance against losing Heskey. Nevertheless, Bruce has remained defiant that he will not lose two players.
"I am the manager of a club that is always going to lose our better players when the big boys come in," he said. "But I won't be losing two players this month, this for sure."