"Basketball, it's always about basketball. Never about rugby," Arnold said grinning.

"Maybe I should get a few basketball shirts made up and walk around in them. One time I went along with it when this person was loving talking to me about basketball.

"I said I played and everything, but I couldn't keep a straight face. They don't even think I'm a rugby player."

That will change when Arnold makes his international rugby debut and becomes the tallest player in Wallabies history when he runs out against England on Saturday night.

He says his height is just a number, but he's promised to use his 208-centimetre frame to make the most of his first chance to wear Wallabies gold.

It caps off a remarkable journey from bush footy, where he was plucked from the pub to play third grade, to the ACT Brumbies and now Australia.

Legend has it Arnold turned up to his first training session without boots because he couldn't find any to fit his size 16 feet.

But what actually happened is Arnold had a pair of boots with moulded studs from his rugby league playing days and his coach called a Queensland Reds player to see if he could lend Arnold some boots with metal studs.

The Reds player was Rob Simmons, and in a bizarre twist Simmons and Arnold will stand side by side for the Wallabies at Suncorp Stadium.

"I always had boots, but not the right ones. Our coach was mates with Rob Simmons and he got him to come down and drop off a pair of [steel-studded] boots for the game," Arnold said.

"But Rob brought them over and I looked at them ... they were too small – size 13 or 14 or something. It's funny how it all works out and now we're playing together."

The laid back Arnold is soaking up all of the experiences surrounding his first Wallabies cap after being told by coach Michael Cheika he was being thrown into the Test cauldron.

Arnold says he still misses his club rugby days with twin brother Richie and the three-hour bus trips to games with their mates.

But his imminent Wallabies debut has given him chance to reflect on the journey that has taken him to the top.

The 25-year-old was unknown in Australian rugby circles last year when the Brumbies signed him following a stint in South Africa's Currie Cup.

His size meant he immediately stood out, and the physical nature of his game put him straight on Cheika's radar.

The raw second-rower won the Australian Super Rugby rookie of the year award last year and was part of Cheika's Wallabies squad, but he was cut from the World Cup team.

"There's no way I would have thought I would have a chance to play for the Wallabies when we were running around in third grade. It's pretty cool how it all panned out," Arnold said.

"I wasn't even thinking about the Wallabies last year so that's all a surprise and it's still sinking in.

"It doesn't faze me having the number 208 [centimetres] around or the tallest Wallaby or whatever. It doesn't mean too much, it's just a stat in the end.

"I just want to get out there and play."

Arnold didn't start to tower over his classmates until he was 17 years old.

Back then he was playing basketball and rugby league with his mates for fun with no thought he could use his size to launch a sporting career.

Cheika wanted him to be a physical force in Super Rugby, and his work has paid off.

"But I'm not nervous yet. I probably will be when the game gets closer and closer," Arnold said.

"Everything and the journey comes flooding back when you get told you're going to be making your Wallabies debut. It brings a bit of a smile to your face.

"You remember where you came from and everything that happened. I loved playing third-grade rugby out in the bush, the boat races and the bus trips. I never took rugby serious at all, it was just a social event on the weekend.

"We had a good time on a Saturday night after a game, then I got asked to take it a bit more seriously. I still miss those bus trips, but you enjoy it for different reasons now. I won't be doing anything crazy [against England], I'll just do my job."