James Ryan must show his leadership "presence" right from the start of his Test career, according to Ireland captain Rory Best.
Powerful Leinster lock Ryan will make his first Test start on his fourth cap when Ireland host Argentina at Dublin's Aviva Stadium on Saturday.
Ryan will partner Iain Henderson in a second row unit of rich potential, but skipper Best has challenged the 21-year-old to set the Test-match standard right now.
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"James Ryan doesn't want a lot for physicality, and that's hugely impressive at his age," said Best of the fast-improving former Ireland Under-20s captain Ryan.
"The hardest thing is to go out and impose your own game on the opposition.
"What we've told him is that it doesn't matter how old you are, just go out and show us what we've seen from him with Leinster and the Under-20s.
"He's a genuine physical presence, and there aren't too many of them in Ireland.
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"We're getting better at producing them but the gene pool is a little bit smaller than, say, the likes of South Africa who naturally have a lot of big men.
"You're born with that physical presence but it's making sure we get the most out of that.
"There's no point being this big, physical character if you go into your shell.
"We've seen bits of it and the fact he captained the Under-20s shows that he's a big character and it's important we get that out of him.
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"It mustn't just be that he fits in, it's that he must fit in, but add something as well.
"We want him to fit in, and we want him to make a difference as well by playing his own game.
"But we also want him to be contributing as a leader. And I've no doubt that from the early signs, that will come."
Stalwart hooker Best will move fourth outright on Ireland's all-time list of Test-match appearances on Saturday, edging past John Hayes on the occasion of his 106th cap.
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The 35-year-old insists Ireland have long since moved past the humbling 43-20 loss to Argentina in the 2015 World Cup quarter-final – and that Joe Schmidt's men have improved markedly in the intervening two years.
"In the immediate aftermath we were very disappointed, but that was two years ago," said Best.
"It was a disappointing day for Irish rugby, but two thirds of this Saturday's starting team weren't there.
"We hope that we've improved our depth and that we never get into that situation again.
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"We got lucky with injuries in the two years in the build-up to the last World Cup and so weren't forced to build some elements of depth.
"But since then our hand has been forced a bit, and so it's been about giving people opportunities.
"I feel the squad's in a stronger place now, and that's mainly because people have had opportunities."