He has done just that - but as a goalkeeper!
And certainly as his former coach at Ringmahon Rangers declares: "He is the biggest thing to happen to Cork since Roy Keane."
Eddie Harrington helped guide Kelleher for nine years at the Mahon club.
Like everybody else connected with the place he'll be glued to the box today, watching him as he faces Chelsea in the EFL Cup final.
Jurgen Klopp has promised the 23-year-old that honour, instead of plumping for No 1 Alisson.
Kelleher began making his name at Anfield back in December 2020, when he starred in a 1-0 Champions League win over Ajax with the Brazilian injured.
Now he has two senior caps and is clearly going places, yet seven years ago the last thing Harrington thought was that he would be making that journey as a goalkeeper.
But a vacancy between the sticks for the under-14s came up, and Kelleher's dad Ray suggested his son fill in.
To the consternation of the youth club's coaches, Harrington took a chance on him.
The rest is not exactly history, but Kelleher is getting there as he goes for the first major trophy of his blossoming career.
Harrington, having taken that chance on risking his star striker, now knows his instincts were bang-on and declares:
"Almost from the first moment we all realised that Caoimhín was a complete natural in goal.
"To be honest, when his dad suggested the idea I was against it - he'd get us 20, 30 goals a season, no problem.
"So I was loathe to give him a try and actually, in his first game, we lost 1-0 and he got chipped.
"But after that he just got better and better - and now look at him.
"Everybody at Ringmahon is so proud of what he's achieved - once he settled in goal, we always believed he was destined for great things."
Another Ringmahon coach back then, Rob O'Leary, admits he was gobsmacked when Harrington stuck his star front man in goal.
He says: "Up front, he was pure class - and we all thought he'd make it as a pro.
"So when he went in goal I was saying: 'what in the name of God is he going in goal for?'
"But I remember I went to see one of his games and, Jesus Christ, he was even better in goal than he was outfield.
"I couldn't believe it." Kelleher himself, however, could.
At the Ringmahon ground that sits on the banks of the River Lee, he set himself the highest standard - and the bar for him was German superstar Manuel Neuer.
He declares: "I like Manuel Neuer, the way he plays football.
"He is good with his feet, the same as me because I was outfield. I like coming off my line.
"I would do that a good bit. I think you have to do that in the modern game."
Boss Klopp revealed that it was exactly those attributes that made him take a chance on Kelleher in the first place, saying:
"We like the football-playing ability, the natural football playing ability of 'Kweev'.
"Of course, he's a really good shot stopper as well.
"They are all calm in the moment when they get the information when they are going to play but there's a difference to be that on the pitch."
Kelleher, in fact, came across as icy-cool right from the start and has only hastened his rise.
No surprise, again, to Harrington who says : "He's still got that baby face, calm and innocent-looking.
"But there's steel inside him, even if he may come across as being quiet.
"In fact, when he's with us, or when he was amongst his playing pals here he was an assassin with one-liners.
"He'd stop you dead in your tracks with what he'd come out with."
Kelleher is not the only sportsman in his family. Brother Fiacre, who first signed for Celtic, was playing centre half for National League side Wrexham and losing 1-0 at the same time as Caoimhín was making his big breakthrough against Ajax. He is now with Bradfiord City
Another sibling, Tim, is a scratch golfer and a third brother, Olan, was a top junior at hurling. Yet as Harrington and his coaches quickly realised, it was their striker-turned goalkeeper who was destined for stardom.
He spent time at Blackburn and Aston Villa and long before he forged his way into Ireland's under-21 side he might even have followed Keane from Cork to Old Trafford.
Not only were Manchester United interested, but Arsenal, too. Yet Harrington recalls: "Once Liverpool came in for him that was it - decision made for him.
"And one day he'll be the No 1 at Anfield - I'm sure of it."