Shaun Longstaff won 15 caps for Scotland between 1998 and 2000

"It's definitely a game of how big can we get them, how quickly, and let's see if they can cope - otherwise, we'll move them on."

Shaun Longstaff, the former Scotland wing turned international rugby agent, might be talking about broiler chickens or beef cattle, livestock and commodities, rather than professional sportsmen.

But this is the ruthless business of modern rugby at the elite end - and the source of Longstaff's alarm.

His agency represents some of the sport's top global talent. Scotland internationals Tommy Seymour and Pete Horne, Ireland duo Conor Murray and Simon Zebo, England's Dan Cole, and Australian Will Genia are among the more illustrious names on his books.

Longstaff, 44, has seen the game change, watched players pump themselves bigger and stronger. He's observed the physical toll - the enforced retirements, the frightening and lingering symptoms of concussion.

He seeks the counsel of surgeons and scientists, and finds himself holding increasingly frank exchanges with his players about their quality of life after rugby.

And he worries about his role in it all, the path his sport is treading, and what might become of those whose careers and well-being he oversees.

'Find us a freak - and cheap'

Leone Nakarawa's unique skill set established him as one of the world's finest locks

Nobody had heard of Leone Nakarawa when the giant Fijian lock first pitched up at Glasgow three years ago.

Such was his astounding skill set, so utterly different to anyone else in his position in this hemisphere, that he left the Warriors this summer a Pro12 winner, World Cup star and rugby phenomenon bound for a lucrative contract with Racing 92, the French champions.

In Paris he joins forces with one of Longstaff's clients, the preposterously proportioned Tongan-New Zealander, Ben Tameifuna, a dump-truck of a prop who tips the scales at almost 150kg (23st 8lb).

There are more Nakarawas and Tameifunas out there to be plundered, hidden gems scattered across Fiji, Samoa and Tonga, and Europe's elite want one of their own.

"Some of the clubs knew we were going on a scouting trip to the islands in April," says Longstaff.

"They weren't looking for a playmaker, or a great kicker, because you can coach a great kicker - they were looking for something they couldn't get over here.

"'Find us a freak'. Someone big and fast and powerful. And they want them cheap, because it is business, and they know if they go to the islands, where poverty is rife, you can pay very little really and get someone over who might come through very quickly."

Longstaff represents gargantuan prop Ben Tameifuna, who weighs more than 140kg (23st)

'Blind-side them at the breakdown'

Amid the myriad analysis tools now used in elite rugby, many sides kit their players out with wearable sensors.

The thirst for more data and enhanced intelligence is a tenet of professional sport, and these gismos measure the G-forces generated when players collide, make a tackle, or hit a ruck.

But Longstaff warns the glorification, and quantification, of the "hit" fuels a dangerous cynicism seeping into some players' psyche.

"There are coaches who openly talk about the G-force on the hits," he says. "Some coaches are now reading and comparing them, in terms of whether they're hitting that ruck hard enough, or carrying hard enough, so effectively they're picking - which kills me - connected to how hard your Gs are on your hits.

"To me, that seems mad, that it's affecting the way you look at the game. If you haven't got the ball, you shouldn't be looking to think, 'there's a dead ruck, so if I hit that really hard, my Gs are going to be really high'.

"But it comes into their heads because they want to get picked, and if they get picked for that game, they might get that new contract. I've definitely seen that taking place, which is a concern."

Longstaff says some coaches talk of inflicting "violence" at the breakdown

Some coaches, says Longstaff, go further. The chaotic and perilous 'breakdown' is an environment in which an opponent can be taken out of the game.

"The main theme is violence at the breakdown for certain directors of rugby," he says. "I've played the game, I know it's a tough game, but that is a key focus for some. That's where they think they can get that edge.

"They want guys hurting the opposition at the breakdown because it's the one chance you can really blind-side someone."

'They all feel bullet-proof'

Longstaff experienced the surgeon's scalpel almost as often as he donned a Scotland jersey in his own career.

Over a decade after hanging up his boots, he says the changes in the game and the shape of those who play it now make physical damage a constant threat.

"I've had two operations on my right shoulder, one on my left, a serious operation on my right hip, three operations on my knees," says Longstaff.

"If you tell any non-rugby person the amount of operations I've had as a 44-year-old, their eyes pop out of their heads. They think it's absolute madness.

Longstaff had spells with Castres and Pau in France after leaving Scottish rugby

"And then I explain to them I was the wimp on the wing who couldn't tackle a fish supper - I wasn't exactly putting my body into awkward positions very often.

"Fast-forward 20 years to what these guys are doing now. It is a different world, and they're doing it regularly. Is their quality of life going to be affected long-term?

"I always tell them to go into this with your eyes wide open, because they all feel bullet-proof. They're in an environment where everyone's bullet-proof; they're so tough."

'Almost every player is not 100%'

With the enhanced physicality comes a vital emphasis on recovery. But Longstaff tells of international players given until minutes before kick-off to prove themselves ready for battle.

"Maybe rugby is on a different level physically because of the way you have to put your body on the line, and the way almost every player is not 100% when he plays," he says.

"I've seen players go into Test matches where the management give them right until the final hour to prove their fitness, which we see more and more often these days.

"Is that the right thing for their bodies, long-term? It is things like that I sometimes find myself saying to players."

Players being taken off on a stretcher is a familiar sight in the professional game

If all this plays out at the top end of the sport, a little way below, youngsters graft to make the physical strides necessary to carve out a professional career.

"There's a massive number of players under the age of 21, 22 that were turfed out of academies last season," notes Longstaff.

"Huge numbers of guys just get moved on. And they have been changing the shapes of their bodies for maybe six years. They would actually look quite odd walking around town now.

"You've built this body, but then what do you do with it? You've got to manage it and live with it. That's their choice - they've gone into this to get bigger, but the pressures to get bigger are huge. Because if you can't get bigger, it's such a tough road to get through."

Brawn and brain - and professionalism

The consensus among leading scientists and doctors is that rugby is gradually addressing the intricate threat of injuries to the brain.

Scottish Rugby's top medic, the immensely-respected James Robson, told BBC Scotland in June that awareness and willingness to take concussion seriously is "massively better" now than in recent years.

Scotland's James Robson has worked at six World Cups and on six Lions tours

Rugby's governing bodies say that is the reason for the increased instance of concussion reported in each of the past five annual injury audits external-link undertaken on England's Aviva Premiership.

But earlier this year, John Beattie's BBC Panorama report investigated chronic traumatic encephalopathy (CTE), external-link a form of dementia caused by repeated head trauma. It has been found in the brain tissue of deceased boxers, NFL athletes, and now, rugby and football players.

There is also a study in progress at the University of Glasgow, examining the long-term effects of concussion in former Scottish internationals.

Meanwhile, Scotland's current fly-half Finn Russell has still to return to contact training three months after the severe head injury he incurred on Pro12 duty for Glasgow Warriors.

And just last week, in the first case of its kind, the former Sale scrum-half Cillian Willis is suing the club for alleged clinical negligence over the concussion that ended his career - a development that has some of England's top coaches fearful of the precedent it could set.

Ex-Sale Sharks scrum-half Cillian Willis is suing the club over concussion

'Did you know about this?'

Longstaff is deeply troubled by this tumult. He, like Robson, is encouraged by the shift in mind-set, but worries his players are unwittingly part of an experimental generation.

They can't know what they're getting into since the science to tell them does not yet exist. But some are already suffering.

"I think the attitude to concussion is improving," he says. "It's more accepted and far cooler now to say, 'I'm not alright', and get off.

"That's one level. The next level is professionalism, and it's ironic, because I represent money and professionalism in the game really, and money comes into it.

"These guys are thinking, 'if I don't play, I might not get that match payment' - some players will think along those lines - or 'I'm coming out of contract, and if I don't play this game, there's a break for three weeks, and then I'm coming into negotiations, I've got to play, and I've got to play really well'.

"The kids play and have different social pressures, and the professional men play and are concerned about livelihoods.

"I wouldn't consider myself some great mind in terms of changing of the laws - I don't know the way forward, I just know that I'm worried, and have been for ages.

John Shaw describes living with "cut-out moments" when his mind wanders

"I'm not sure there's a lot of knowledge there for players. I find myself sometimes offloading my own conscience a little bit - I talk to every player about their thoughts on where the game's going with regards to the protection for the brain.

"I'm their agent; I've been with some of these guys for 12 years now, so I have witnessed the physicality modern players face in the changing game.

"Have I done enough? Because if they go into their 40s and 50s with head problems - whether it's just headaches, which might be the lesser symptoms, or it's worse than that - it wouldn't sit well with me.

"I don't want to be an old man, and some of these players are 15, 20 years younger than me phoning me and saying, 'did you know about this? Because I can't remember what I did yesterday, and I can't hold down a job'."