Toomua also says Wallabies rivalries will add extra spice to an Australian derby against the NSW Waratahs, but insists it won't be a motivating factor at Allianz Stadium.

Wallabies and Brumbies player Toomua has been cleared to play against the Waratahs after suffering a minor concussion last weekend.

Toomua was concussed twice in back-to-back weeks while playing for Australia last year, which led to him taking a month of training to get his health right before the end-of-year spring tour of Europe.

But Toomua says he won't hesitate throwing himself in front of the rampaging Waratahs in Sydney, confident the injuries aren't related and there will be no ongoing issues.

"It was only a small incident [last weekend], a few decision making things were a little bit off and you can't get away with that [at five-eighth]," Toomua said.

"The head knocks don't affect confidence at all. I passed all the tests but I was a bit slow and came off.

"This game is going to be a good test for us ... the reigning premiers at home, with respect to other teams, it's going to be one of the biggest tests you get."

The competition for Wallabies World Cup selection adds extra intrigue to the Brumbies-Waratahs contest.

The Super Rugby season is only in round six, but players have a chance to impress Australian coach Michael Cheika and his World Cup assistants, Stephen Larkham and Nathan Grey.

Of the 30 players who will start the match, 22 have played for the Wallabies and all will be keen to secure a World Cup berth at the end of the year.

Even Toomua is excited by the one-on-one battles, but is confident neither team will lose sight of their mission to win.

"Your head's in the sand if [a Wallabies place] is not in the back of your mind. We're all thinking about it, but we all know that we have to take a first step," Toomua said.

"There are so many mouth-watering clashes across the 15, not just in the backs. There are some great match-ups in the forwards as well and it's exciting from a watching point of view. I'm lucky to be a part of it."

The Brumbies have failed to score more than eight points in each of their past three matches against the Waratahs in Sydney.

The most recent was a 29-8 loss to the Waratahs in the Super Rugby semi-final last season.

Toomua said the Brumbies were wary of the Waratahs' dangerous attack, warning that the star-studded backs will "have a field day" if the Brumbies aren't ready in defence.

The Brumbies have scored 18 tries in their five games this season, while conceding only three in defence.

"Of course last year stings, but the Waratahs deserved to win. It can be a bit of motivation, but it's a new year, you've got to get past it," Toomua said.

"You've got to give the Waratahs respect, they are the champions. But you don't need heaps of extra motivation against Australian teams."

SUPER RUGBY ROUND SIX

Sunday: NSW Waratahs v ACT Brumbies at Allianz Stadium, 4.05pm. TV time: Live on Fox Sports 2.

Brumbies team: 15. Robbie Coleman, 14. Henry Speight, 13. Tevita Kuridrani, 12. Christian Lealiifano, 11. Joseph Tomane, 10. Matt Toomua, 9. Nic White, 8. Ita Vaea, 7. Jarrad Butler, 6. Scott Fardy, 5. Sam Carter, 4. Rory Arnold, 3. Ben Alexander, 2. Stephen Moore, 1. Scott Sio. Reserves: 16. Josh Mann-Rea, 17. Ruan Smith, 18. Jean-Pierre Smith, 19. David Pocock, 20. Jordan Smiler, 21. Michael Dowsett, 22. James Dargaville, 23. Lausii Taliauli.

Waratahs team: 15. Israel Folau, 14. Taqele Naiyaravoro 13. Matt Carraro, 12. Kurtley Beale, 11. Rob Horne, 10. Bernard Foley, 9. Nick Phipps, 8. Wycliff Palu, 7. Michael Hooper, 6. Jacques Potgieter, 5. Dave Dennis, 4. Will Skelton, 3. Sekope Kepu, 2. Tolu Latu, 1. Benn Robinson. Reserves: 16. Hugh Roach, 17. Jeremy Tilse, 18. Paddy Ryan, 19. Sam Lousi, 20. Mitchell Chapman, 21. Stephen Hoiles, 22. Brendan McKibbin, 23. Jono Lance, 24. Peter Betham.