While Knoyle might largely remain an unknown quantity outside Wales, the fact he has relegated Mike Phillips to bench duty this weekend should make people sit up and take notice.
Phillips, one of Welsh rugby's biggest names who was the British and Irish Lions Test scrum-half in South Africa three years ago, has 61 more caps than Knoyle, who has made seven appearances so far.
But 22-year-old Knoyle impressed Wales' coaching staff during last week's punishing training camp in Poland - which Phillips missed due to club commitments in France - and he has now been handed a golden opportunity.
"I am chuffed for Tavis," said Priestland, who plays alongside Knoyle at the Scarlets.
"He is such a well-liked character within the Wales squad and the Scarlets squad. He is a larger-than-life character and everyone feeds off his enthusiasm.
"What's great about Tavis is that he always wants to learn and improve himself. He has been playing well for the Scarlets, and it is great for him to get a chance on Saturday."
Priestland has little doubt that Knoyle will be seen - and heard - in an opening autumn fixture that is followed by Millennium Stadium appointments with Samoa, New Zealand and Australia.
"Tavis shouts a lot on the pitch," Priestland added. "He has a high-pitched scream that he aims at the forwards!
"His understanding of the game is getting better all the time, and he shouts at the forwards, which is what you need from a number nine.
"He is one of the fittest players in the squad and he gets to breakdowns quickly. As a 10, all you can ask is that the nine gets the ball away, and he does that well.
"He is a big strong boy, and a lot of people have made comparisons between him and Mike. Hopefully, he will go well on Saturday.
"They are both physically-gifted players, although I don't think you can compare them. Mike has got a wealth of experience, and I am sure Tavis looks up to Mike."
Knoyle's selection is one of seven changes from the Wales team beaten 20-19 by Australia on their last outing almost five months ago.
Given the consistently-impressive form of Ospreys playmaker Dan Biggar this season and James Hook's continued excellence, Priestland could not take his place for granted despite helping guide Wales to a World Cup semi-final last season and an RBS 6 Nations Grand Slam.
But the 25-year-old revealed he is not one to get caught up in the often mind-warping worries of selection.
"It was quite strange," he said. "I didn't really think about it (selection). You do everything you can do, and it is not really up to you then.
"When you train you train to do the best you can and try to get into the team and do the best you can. Once selection comes around, though, there is nothing you can do about it.
"When I was first involved with Wales in 2011, I didn't even think I was going to be in the squad. I was gob-smacked.
"I think the lucky break for me was the World Cup warm-up game against England at Twickenham last year when I had a chance to play 10 (Stephen Jones suffered a late injury), because I was down to play full-back that day.
"I train as hard as I can, but ultimately the decision is out of your hands, so there is no point in working yourself up over things you can't control.
"The more time I have spent within the squad the more comfortable I have become with the way we want to play.
"You can't account for every situation in a game, but you learn from it each time."
Wales have won nine of their 13 Tests against Argentina, including when the countries last met in a World Cup warm-up fixture at the Millennium Stadium 15 months ago.
But the Pumas have arrived in Cardiff fresh from their debut campaign in the southern hemisphere's Rugby Championship when their stand-out result was a 16-16 draw against South Africa in Mendoza.
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