What followed was eight of the best minutes a rookie athlete has ever delivered.

He described his mum Helen as a "witch" (in a way that is sure to get him in trouble, but he insists is a good thing) after she booked a family holiday to Melbourne long before knowing of his Super Rugby selection.

"She actually planned a holiday to Melbourne for this exact date and has somehow landed on my starting debut," Hooper said. "We reckon there's a bit of hocus pocus going on there."

He detailed why he gave up two Canberra classics - Goodberry's and Kingsley's - in the off-season to give himself the best chance to force his way into the Brumbies side.

"I was on the chubby end of the lock spectrum," he grinned. "It came down to willpower. If you want something enough, you find ways to make it work."

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He said he enjoyed being thrown in the Super Rugby deep end, with his first five games all being against New Zealand opponents.

"Obviously I wasn't a world beater by any standard, but I knew I could match it at that level," he said of the daunting start to his career against the Canterbury Crusaders.

But mostly, he spoke with so much poise and knowledge it was easy to see why coach Dan McKellar didn't hesitate throwing him into an Australian rugby derby on Friday.

"To fill [the shoes of Wallabies locks] is a big ask, but I definitely want to put my name on the radar."

Hooper, a 21-year-old former junior Wallaby from Bathurst who has starred for the Tuggeranong Vikings, is one of several changes to the Brumbies side this week.

He replaces Darcy Swain, who suffered a head knock last weekend and it was decided not to rush him back into action.

Folau Fainga'a has an injured ankle and will miss at least one week, with Connal McInerney getting his first Super Rugby chance of the season at hooker.

Jesse Mogg replaces Andy Muirhead on the wing, Scott Sio starts at loosehead prop with James Slipper moving to the bench and Sefo Sefo Kautai is on the bench as the back-up to skipper Allan Alaalatoa.

The Brumbies are going to Melbourne trying to continue their unbeaten start to the season after beginning the year with three wins in three games at home.

Hooper has patiently watched and waited for his chance, but he says he's ready to step up now after having to deal with All Black opponents in his professional initiation last year.

Hooper played from the bench in the trans-Tasman series and didn't look out of place. Now he is in the rare position of having that experience after COVID caused Super Rugby scheduling chaos for the past two years.

"This is actually the first time I've actually come up against an Australian opposition," Hooper said.

"That'll be a nice change ... playing against guys I used to play with in the [Australian under-20s] rather than All Blacks.

"But I took a lot of confidence out of [trans-Tasman games] last year. Obviously I wasn't a world beater by any standard, but I knew I could match it at that level.

"I made some physical adaptations ... get quicker, more plyometric and then take the learnings into the game this weekend."

McKellar has no doubt Hooper can handle the challenge ahead.

"For a young player he's very professional, really thorough with his approach and mature well beyond his years," McKellar said.

"He's got a big engine. He'll run all day ... the challenge we've put to him is to make sure that he's powerful and explosive, and make sure it's quality."

And Hooper took McKellar's request seriously at the end of last year.

He cut out Goodberry's frozen custard and ditched Kingsley's "awesome chips" for a lean diet.

He has dropped seven kilograms so far, weighing in at 118 kilograms for his first start in the Brumbies' lock spot.

"I've gone down in weight but more lean muscle. I was on the chubby end of the lock spectrum," Hooper said.

"I was 125kg ... I put down 122kg on my player profile because I was a bit embarrassed.

"A lot of the credit goes to the strength and conditioning team. I got a lot of one-on-one treatment, they were catering meal plans for me.

"It came down to a bit of willpower ... staying away from Goodberry's and Kingsley's. I think if you want something enough, you find ways to make it work."

But there is a part of Hooper who thinks he might not have needed extra work, because other forces may have been working for him.

Mum Helen and dad Lloyd made the trip to Christchurch last year to watch his debut against the Crusaders.

This year they booked a holiday to Melbourne on the same weekend of the Brumbies game.

"My brother and I actually have a bit of a running joke that my mum's a bit of a witch," Hooper grins.

"She actually planned a holiday to Melbourne for this exact date and has somehow landed on my starting debut.

"We reckon there's a bit of hocus pocus going on there. They'll be there and it'll be awesome they can be there to experience it.

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"She'll be angry at me for saying that, but she knew it was coming."

Hooper is getting his shot because Swain is out temporarily, and the Brumbies are unsure when Caydern Neville will return from a shoulder injury.

They have drafted former junior All Black Hamish Dalzell into the squad on a short-term contract to ensure they have enough second-rowers to get through the early part of the season.

"I think that's where the excitement originates," Hooper said. "Just having that opportunity, having a foot in the door.

"I've just got to make sure I step all the way through the door and take it with both hands. I definitely want to put my name on the radar and put my name up for selection every week."

SUPER RUGBY ROUND 4

Friday: Melbourne Rebels v ACT Brumbies at Melbourne, 7.45pm.

Brumbies: Scott Sio, Connal McInerney, 3. Allan Alaalatoa, 4. Tom Hooper, 5. Nick Frost, 6. Rob Valetini, 7. Jahrome Brown, 8. Pete Samu, 9. Nic White, 10. Noah Lolesio, 11. Jesse Mogg, 12. Irae Simone, 13. Len Ikitau, 14. Tom Wright, 15. Tom Banks. Reserves: 16. Billy Pollard, 17. James Slipper, 18. Sefo Kautai, 19. Ed Kennedy, 20. Luke Reimer, 21. Ryan Lonergan, 22. Rod Iona, 23. Chris Feauai-Sautia.

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