The teenage superboot will join three Canberra juniors as the Brumbies' contingent in the Australian under-20s side for the World Cup in England.

Jooste was on the verge of a Super Rugby debut in the Brumbies two games before he left for the tournament and was only a phone call away from being put on the field while Christian Lealiifano waited for the birth of his first child.

But Jooste is using the rise of under-20s teammate Jordan Jackson-Hope as the extra motivation in his World Cup campaign, which starts against Scotland on Wednesday morning.

Jackson-Hope was a shock inclusion to play against the Melbourne Rebels and Japan Sunwolves, showing he can capably match it at the professional level.

Now Jooste, 18, is keen for his chance after battling osteitis pubis for most of the year.

"It was an awesome experience to be in that Brumbies match-day squad and if I get that chance [after the World Cup] then I'll be looking forward to it," Jooste said.

"The next few weeks are very exciting for me and [Jackson-Hope], everyone made it really easy for us to juggle both under-20s and Brumbies stuff.

"Everyone has been really understanding so I've had a chance to get to know both. I've just got to rip in."

Jooste's year threatened to be derailed by the debilitating osteitis pubis problem. He has been on a modified training schedule for the past three months as he managed his workload and built strength in his groins.

But the Australian coaches see a future star and couldn't resist the opportunity to throw him into the under-20s.

Jooste missed the under-20s warm-up matches to be on standby for Lealiifano.

Jooste is part of an exciting new generation at the Brumbies that includes Jackson-Hope and their Australian teammates Tyrel Lomax and Faalelei Sione, while Joe Powell, Tom Staniforth and Allan Alaalatoa are 22 or younger.

All are expected to get a chance to shine in the Canberra Vikings' National Rugby Championship squad later this year, but the Australian under-20s quartet have international glory at the front of their minds.

And when they return, Jooste and Jackson-Hope will be back at Brumbies training as the team chases a Super Rugby finals berth.

"There's a real belief in Australian rugby at the moment after the Wallabies made the World Cup final last year and we're trying to ride that wave," Jooste said.

"The osteitis pubis is something that hangs around for a long time so it was just about working with it and managing how bad it was.

"I had to make sure the strength and flexibility was still there in my groins. [Jackson-Hope] did unreal in his Brumbies debut and if I get the call-up I'll put my best foot forward."