World Cup countdown: Gerry Thornleyfinds Jamie Heaslip typically relaxed, even philosophical, despite an acute awareness of the huge stakes being played for today

He seems laid back to the point of being prostrate, as the saying goes. Indeed, Jamie Heaslip's pre-match ritual usually involves having a nap on the team bus or wandering off for a walk away from the dressing-room.

That, as he concedes, is how his nerves betray themselves, and come the warm-up and the kick-off, he's as fired up as anybody. But he doesn't tie himself in knots, he's not an avid student of the game, he doesn't go out of his way to watch matches, and he doesn't get worked up about opponents.

"He's not a real rugby nut," says his one-time Trinity coach Tony Smeeth, long since a self-professed fan of the Leinster number eight, "and I think that serves him well actually. He just plays. For example, Ireland were due to play a big under-21 one week when he came up to us for training on a Tuesday or Wednesday. I asked him who they were playing and he said, 'England or Wales.' He couldn't remember."

His nonchalance should serve him well today. In only his third test, the 23-year-old is one of those vying for the last slot or two in the back row. The squeeze is on, not least because coach Eddie O'Sullivan is intent on picking only five backrowers. This could count against specialists such as Heaslip or the Leinster openside Keith Gleeson, though the possibility of Alan Quinlan being named as a backrow-cum-lock might open doors.

Heaslip also talks about Simon Taylor and Ally Hogg, familiar adversaries from Leinster-Edinburgh clashes, and a first clash with the Scots icon and captain Jason White.

"It's going to be a challenge alright and on top of all that it's the first game of the season," he says, laughing off the magnitude of what faces him and his team-mates.

Ever since he was the talisman in Ireland's remarkable progress to the under-21 World Cup in 2004, making this World Cup was a target. Rugby was always in his blood. His father, Richard, played for Shannon and the Irish Army. His elder brothers played too, Richard with Trinity and St Mary's, and Graham for Galwegians and Connacht.

Heaslip attended Newbridge College, and began playing at Naas under-10s: "I could not get enough of it. I remember even when I was sick I insisted on going training. My parents used to threaten me with not playing and that would just shut me up. I'd be as good as gold then. I suppose I always wanted to play because I looked up to my brothers."

His brothers and parents encouraged him to train through the summers, and his father and his mother, Christine, invariably attend his games: "I have a freakish ability to spot my dad in the crowd at nearly every game."

Being a captain in the army, his father provided a disciplined upbringing.

"He was pretty strict with us, though not in a bad way, but there was no messing. My brothers and sister always say he was easier on me because they'd worn him out by the time I was a teenager."

Heaslip first began to think he might be useful at rugby when he was called into a Leinster schools trial at just 15. The following year he made the Leinster schools team and from there the Ireland schools team, progressing to the Ireland under-21s. By then, he was making a name for himself at club level with Trinity, and Smeeth was loudly hailing him as a future star.

Hugh Maguire, the assistant/forwards coach, encouraged Heaslip to run harder at opponents and play a more complete game.

"They were huge influences on me. Trinity's rugby ethos is very attacking, very wide and very fast, and that's the way I like it - a mix of backs and forwards and not too structured. We won a lot of things there, and went from Division Three to Division One."

Smeeth has no doubts that Heaslip was, by some distance, the primary reason Trinity won promotion to the first division: "He can play a wide-ranging game; he can play a running game or a ball-carrying game up the middle, and his work-rate in defence is high. He's a special kind of player."

That Heaslip can seamlessly make the step-up to the next level Smeeth attributes to the player's pace: "Speed is the major denominator, and because he's so quick he doesn't suffer when he moves up another level. He's not fazed by anything. He's an intelligent lad and he's the best player I've ever coached."

It was during the Under-21 World Cup and Ireland's unlikely march to the final that Heaslip shot to prominence with a sequence of outstanding performances. He recalled how Ireland's form snowballed after an unexceptional win over Tonga, confidence rising with each victory - over Argentina, France and Australia - to where they thought they were world beaters, before New Zealand ended the dream in the final.

"It was weird, during that under-21 tournament, because while we were doing well all I really wanted to do was get out to America because all of my friends were in America on J Ones. I was getting emails off them about all the craic they were having out in San Diego. I was going out within two days of whenever it ended for us."

Shortlisted for under-21 player of the year after the 2004 World Cup, Heaslip was expected to start tearing up trees immediately, but in effect he delayed his professional rugby career for a year by completing his degree in medical mechanical engineering in DCU.

His rookie year went well and despite the grave warnings, last season he laughed off one of the game's clichés: "I didn't know what this whole 'second-season syndrome' was. People kept going on to me about it . . . What's this, a fecking disease? I didn't know what they were talking about.

"But I suppose I got a little bit of it at the start of last season, because it went from a pretty intensive baptism of fire in the first year to the Churchill Cup, and I got a pretty short pre-season. So the brain was a little bit fried, but once I got a couple of days off here and there I was fine."

Invariably Leinster's best forward week to week, he was the only Irish forward picked on the Magners League team of the season and, tellingly, was voted Leinster's players' player of the season by some distance.

It goes without saying he'd like a big game today and you feel almost guilty for interviewing him or any of the other players seemingly competing for slots.

"If you put yourself under pressure and start thinking about it, you won't play the game you play," he says. "But it's still hard not to think about it; you're playing Saturday and he's picking the squad on Sunday. It doesn't take a rocket scientist to tell you that it's your last chance."

It won't faze him though.