Scotland head coach Gregor Townsend has handed Zander Fagerson his 50th cap eight years after giving the prop a professional debut at the age of 18.

The Glasgow player will reach his milestone when Scotland take on Argentina on Saturday in the summer tour series decider in Santiago Del Estero.

Townsend noted Fagerson was a “very young age” to reach his half-century, four years younger than 30-year-old Hamish Watson achieved the same feat last week.

And the former Warriors head coach always felt the front-row forward was destined to achieve quickly.

“He was very strong as a 17/18-year-old,” said Townsend, who has made eight changes. “When he first came into the programme, he played really well for the under-20s, and through training and learning, we saw he was getting close to professional level.

“He played well at professional level at a very young age and he had some moments that didn’t go that well for him. I remember Scarlets away, I had a difficult decision to make, when you have to take someone off before half-time, but that did happen to Zander in one of his first outings for Glasgow.

“But you often learn more from those occasions than when you have played at your best.

“But Zander has always been driven to improve, he cares a lot about this team, and he has got extra motivation every time he plays with his brother (Matt). They are bringing the best out of each other.

Zander FagersonZander Fagerson will win his 50th cap (Jane Barlow/PA)

“He has been consistent for us over the past number of years. He brings so much more than just scrummaging, but last Saturday was one of his best scrummaging performances of the season.

“His work in contact is outstanding, world class, and his ball carrying too is a real handful for defences. I am sure he will do all he can to put in an even better performance this weekend.

“There is much more to come from Zander too given his age and experience.”

Glasgow full-back Ollie Smith will make his debut after replacing the injured Rory Hutchinson, who suffered a minor injury in Scotland’s 29-6 victory last Saturday. However, the 21-year-old was already earmarked to start the final Test.

“We have high expectations from Ollie because of the way he has been training, and playing this season for Glasgow,” the Scotland head coach said.

“It suggests he will transfer that form into the Test arena.

“He is one of our hardest workers in training, which is a real trait for a full-back, to be constantly on the move in attack and defence. He has a good left boot as well which gives the opposition something to think about when you have a right-footed kicker at 10. And he is a very good attacker.

“I think he will get a lot of ball. The pitches haven’t been full size here so there are more kicks going into the 22 into full-backs’ hands. We see Ollie playing really well on Saturday.”

Kyle RoweLondon Irish winger Kyle Rowe misses out (Victoria Jones/PA)

Townsend is without three injured backs in all. London Irish winger Kyle Rowe suffered a knee injury which will require specialist advice next week after coming off the bench on Saturday, and winger Darcy Graham has been ruled out with delayed concussion.

Rufus McLean takes Graham’s place, while Sione Tuipulotu replaces Sam Johnson at inside centre and scrum-half Ali Price is recalled.

Rory Sutherland and Ewan Ashman come into the front row, while Scott Cummings and Jonny Gray form an all-changed second row, with Edinburgh lock Glen Young in line for a debut off the bench. Flanker Watson will captain Scotland for the first time.

Townsend admitted that the success of the tour would “probably” be defined by the outcome of Saturday’s game but stressed there had already been major benefits.

“There’s a lot of success on how we have seen players develop, players who got that opportunity against Chile, players who have had opportunities in the last two weeks and who are going to have opportunities this weekend, and from how well they have learned and trained during this period,” he said.

“The success off the field, this group coming together, leaders emerging. Hamish has gone from someone who hadn’t been in a leadership group before to vice-captain and now captain.

“But ultimately we are here to win games and finding a way to win is what we are tasked with doing this week and during the 80 minutes.”