Cahill lifted the lid on his disappointment at the broken jaw that cost him the chance of playing in his first major international tournament in the middle of what has been a rollercoaster 2012 for the 26-year-old.
With a month of this year still remaining, Cahill is already on his third Chelsea manager, having only joined them in January, and his second England boss.
He won the Champions League and FA Cup and was part of a squad tipped to be crowned this season's Barclays Premier League champions.
But he now finds himself at a club rapidly losing ground at the top of the table and on the brink of surrendering the European Cup.
He even faces a fight just to reclaim his place for club and country but nothing has hurt him more this year than the injury he suffered on the eve of Euro 2012.
"It was the biggest blow and I haven't spoken too much about it," said Cahill, speaking at the second annual England Footballers Foundation Charity Cup.
"It really was for me because I knew it was an opportunity.
"I had a lot of confidence leading off the back of what we did last year and really looking forward to going to my first major tournament, and it wasn't to be because of that.
"So it took me a few weeks to get my head around it.
"It's hard. I think if you ask any player, when you're injured, even if you're just injured for a Saturday game and you go to watch, it's not the same.
"You're always itching in the stand and you're thinking, 'I should be out there'.
"So to miss a major tournament is like that times 10.
"So it was a difficult time and, like I said, a big blow in my career but one that I hope makes you stronger.
"Now, my main goal is the World Cup and I'm more focused than ever to try and make that."
Cahill's first challenge is to convince Rafael Benitez he merits a place in the Chelsea side after illness prevented him starting the Spaniard's first game in charge.
The interim Blues boss stuck with the same defence that kept a clean sheet against Manchester City in Wednesday's goalless draw over Fulham but suspension for David Luiz means Cahill is almost certain to start Saturday's game at West Ham.
Like many of his England team-mates, Cahill will be desperate for regular first-team football to ensure he does not slip out of Roy Hodgson's England squad.
Cahill said of the man who succeeded Fabio Capello as Three Lions boss: "He's used quite a lot of players in the last few squads so I think that's a good thing and he's slowly putting his point across.
"I think in the next few months, everyone is aware of what is expected of him now but especially with him seeing first hand in the squad quite a few players now, I think that's been good."
England face a fight just to qualify for the World Cup in Brazil, having surrendered top spot in their qualifying group.
But Cahill was confident the young players who have been introduced to the set-up under Capello and now Hodgson would improve further in 2013.
He said: "I think from the last squad that you've seen, there was a lot of young players in that squad, so we've another year or so experience with that for all of us and it stands us in good stead.
"Going into any tournament, you've got a realistic chance of winning it. We just hope that we can actually do it."