"Come on, you weak dog," the returning Wallabies back-rower bellowed to himself inside the North Queensland Cowboys' state of the art gym.

Perhaps we should expect nothing less from a man who prides himself on physicality, a man who spent two weeks living in "a glorified jail cell" preparing for his return to Test football.

Now 27-year-old McMahon wants a chance "to see if I'm still capable of standing up with the big dogs".

McMahon is on the verge of playing his first Test match in almost four years should he get the nod from Dave Rennie to face Argentina in the Rugby Championship in Townsville on Saturday.

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Rennie concedes it is a pity Australian rugby fans have largely missed out on seeing McMahon over the past three years following his move to Japan's Top League with Suntory.

But he is primed to shine as he joins a resurgent Wallabies outfit, with Rennie saying McMahon may well be the fittest man in the squad despite coming out of hotel quarantine before linking up with the team.

"I was just basically living in a gym for two weeks," McMahon said.

"The day consisted of me getting up and knocking out two or three hours of training in the morning, having a little snooze and some lunch and then jumping back on the bike for about 10km in the afternoon.

"There's not a lot to do when you're stuck in a room. It's kind of like a glorified jail cell."

McMahon has played 26 Tests for Australia and returns to the fray with many among the Australian rugby scene hopeful his best years are still ahead of him.

Loosening of the Giteau Law would allow McMahon to continue to play club football in Japan but feature more often for the Wallabies, who have risen to No. 3 in the world rankings following the returns of Samu Kerevi and Quade Cooper.

"Everyone misses throwing on the gold jersey when they don't have the chance to put it on anymore," McMahon said.

"Dave and me were talking on and off about trying to get me back and things just kept falling out of place with things in Japan, Australia, stuff like that ... COVID didn't help, that's for sure.

"It's always nice to know that there are people and coaches around that still want you to be back and ... have a crack.

"It just gives you more motivation when you're overseas. For me, to train and make sure that I was up to scratch if there was ever an opportunity for me to come back."

McMahon offers the Wallabies another back-rower with a relentless style of play, and says a stint in Japan has done wonders for the body of a man who could "nearly classify myself as an old bull now that there's so many young faces around".

"I'm feeling fresh and it's been good for me up in Japan ... it's a very fast game and I am looking forward to the contact side of things back at international level to see if I'm still capable of standing up with the big dogs," McMahon said.

"There's plenty of competition especially in this environment at the moment, a lot of youth and then you've got the experience of Hoops.

"It pushes you to want to learn quickly and get your head around everything. Those boys have been more than willing to help me out and try to get my knowledge up to speed as quickly as possible."

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