Throwing a 21-year old rookie into a crucial World Cup match against one of the host nations on the other side of the world might seem like a risk to some.

But it’s exactly the type of challenge Sean McMahon thrives on.

Replacing the suspended Michael Hooper for Sunday morning’s Pool A decider against Wales, McMahon has big shoes to fill, but he certainly won’t be overawed by the occasion according to his coach.

“Sean doesn’t care much for those sort of things,” Melbourne Rebels coach Tony McGahan told Rugby News.

“The great thing about Sean and what sets him apart from others is that he just keeps it simple. It’s rugby, it’s footy, it’s what he loves and it’s what he enjoys, he just loves to compete.”

McMahon’s journey to the World Cup has been short, but tremendously impressive. He missed Schoolies after graduating from Nudgee College to join the Australian Sevens program, before being picked up by the Rebels a year later.

“We didn’t have any expectations on Sean when he came into the program, he missed the 2014 pre-season because he was with the Sevens program and he’d only played two games of 15-a-side rugby in 2013, so we looked at him as someone that might come into calculations later in the year.” McGahan recalled.

“He came down in January and immediately impressed in the four weeks leading into our first trial an we ended up starting him in round one against the Cheetahs, so the impact he made in that short time was really impressive.”

And that’s when things really took off.

In 2014, he made his Super Rugby debut, captained the Australian U20’s, was named NRC player of the year with the Melbourne Rising, won the Super Rugby rookie of the year award and earned a spot on the Wallabies Spring Tour, making his International debut late last year against, ironically, Wales.

“That’s certainly no surprise to anyone who’s been at the Rebels for the last two years and seen what Sean has demonstrated both training wise and with what he has delivered on the pitch over the last two years,” McGahan said.

“From the first day he came into the program he’s worked exceptionally hard, he hasn’t worried about number of games, profiles, achievements, he’s just rolled his sleeves up and got stuck in every day.“

Whilst McGahan feared the dreaded ‘second year syndrome’ might affect his young star, McMahon returned from his time with the Wallabies with more hunger than ever before, continuing to be just as impressive off the field, as he was on it.

“That all comes down to his family, they’ve been a tremendous support for Sean,” he said.

“It’s not easy for a guy that young to move to another city and make it work and function without a lot of support there, so he’s obviously done a great job but really it’s the family nucleus that has provided that support and made it work.”

With a surplus of talented backrowers flooding the Australian rugby ranks, McMahon’s promotion to the Wallabies No.7 jersey is testament to both McGahan and Michael Cheika’s faith in the 21-year old.

“He’s got strong capabilities of playing No.7, as he’ll do this weekend at international level, but that is different to Super Rugby. He plays No.6 here at the Rebels and we’d also like him to play a bit of No.8.”

“When you look at the players in the game now, McCalman, Higginbotham, Pocock shifting back to No.8. You’ve got to find a way to get you best players on the field and make it work.”

Facing the toughest test of his short career against Wales this weekend, McGahan has no doubt McMahon is up for it.

“He just seems to thrive in the tougher environment, he just excels anytime you put a challenge in front of him.”