The 22-year-old believes he would be wasting his time if he didn't "have a dig" – something embodied through his crash and bash style of footy - and has a message to any teammate who wants to go ahead of him in the pecking order as Australia's next long-term No.8.

Good luck, it's not going to be easy.

Michael Cheika has instilled faith in McMahon by naming him to start at the back of the scrum on Saturday (Sunday AEST) against the Springboks in Pretoria.

McMahon has only started at No.8 twice in his Test career – both times against England in June – given he is a No.7 by trade but says there is not a chance he will let this opportunity slide.

"There's players like Lopeti Timani and that who could easily lock that role down or take it from me but I can tell you it's not going to come easily - they're going to have to work for it," McMahon said. "There's always a lot of talk at the moment when it comes to me that I'm not tall enough to be a six, not big enough to be an eight. I don't fit into all the roles but I'm a bit of everything. Any opportunity to throw on the gold is an opportunity and if eight's going to be that opportunity, I'm going to be taking it with both hands."

Australia's regular No.8, David Pocock, will make a return from hand surgery in either the All Blacks game in Auckland or for the Spring Tour.

Although it means McMahon will have to step aside, someone needs to fill in for Pocock when he goes on a sabbatical next year as well as  beyond the 2019 World Cup at some point.

It is fitting that the tattoo McMahon got when he was 18 years old and just cutting his teeth with the Melbourne Rebels holds so much meaning.

"Life's not a whole heap of time," McMahon said. "If you're not willing to have a crack and have a dig, you're not going to get anywhere. It's probably what I take into rugby. If I'm not going to be out there having a crack, what's the point in playing?

"It's another opportunity to put on the gold jersey. It's going to be something special over here and especially at Pretoria. [I'm] speechless. It's going to be one of the biggest physical battles of the year probably."

McMahon has been wearing a sleeve at training this week to protect a new eye tattoo on his elbow.

As for the meaning behind it, he says: "Let's be honest boys, there's a few things on here that don't really mean much, we're just filling her up at the moment."

And if McMahon keeps going the way he is with a can-do attitude, he'll only fill Cheika with more confidence that he can be a reliable weapon at No.8 going forward.

"I just like his attitude, he's a strong running player," Cheika said. "He's fearless and he's got really good energy around the team."