Since his £5 million move from Villa Park in January 2008, Cahill’s excellent form has caught the eye of England boss Fabio Capello, who has drafted him into his last three national squads.
And Cahill, who has arrived with his fellow England team-mates in Ukraine for Saturday’s World Cup qualifier, believes O’Neill dropped a clanger by letting him go to the Reebok Stadium.
“Martin O’Neill is a great manager. But everyone makes mistakes sometimes and he’s moved on," he said.
"They’ve brought in some good centre-backs now, they’re doing well and, like I say, everyone makes mistakes.”
Allowing Cahill to leave and then splashing out £8 million on Curtis Davies appears to be one of those mistakes, especially as, on current form, the 23-year-old is England’s best central defender.
In stats compiled by Castrol Analysis, the Bolton defender has made more clearances, tackles and interceptions than John Terry, Rio Ferdinand, Matthew Upson and Joleon Lescott.
And if Cahill can maintain this form over the whole season, he could well prove to be England’s surprise package in South Africa.
Cahill believes his decision to seek regular first-team football was the right one for his career, and there is no bitterness about his departure from the Midlands club.
“It was agreed that it was best for me to be playing week in and week out, and it’s worked out for me," he said.
“He [O’Neill] never forced me out of the door. I spoke to him a few times and at that present time he couldn’t guarantee me a place.
“I can’t do anything sat on the bench and I’ve improved a lot from my days at Villa. It could have backfired on me but it’s turned out to be good decision for me and my career.”
O’Neill on the other hand may well be regretting his decision, especially having had to bring in more costly defensive reinforcements in the form of £6 million man Richard Dunne and James Collins for £5 million.
And the figures Villa have spent to bolster their back-line since Cahill’s departure justifies the fee Bolton manager Gary Megson agreed to pay for the Yorkshireman’s services.
“When he paid £5 million some eyebrows might have been raised at that, people might have thought ‘what has this lad done?’” Cahill said.
“He took a gamble but I hope it has paid off.”
With Manchester United, Arsenal, Spurs, Real Madrid, Barcelona, AC Milan and Juventus all thought to be prepared to pay up to £20 million for the Bolton stopper, Cahill’s form has already forced Megson to warn interested clubs off his prize asset.
But Cahill, who recently extended his contract by a year, is not being distracted by rumours of a move to a bigger club, focusing only on his England ambitions.
“Playing for England has always been the level I wanted to get to. For everyone who has been in a squad, that has to be the target. It’s the chance of making the World Cup.”
