But assistant coach Stephen Larkham is confident the Brumbies' back line can match it with the Waikato Chiefs' potent attacking weapons, even if Toomua is unable to play in Tauranga on Friday night.

The Brumbies will learn today whether Toomua has a serious injury to his knee or whether he can guide the team into the round-four match.

He felt a strain just 10 minutes into the Brumbies' 24-23 victory over the Free State Cheetahs two days ago, but stayed on the field for the remaining 70 minutes as they clinched a last-gasp victory.

If he is unable to play, the Brumbies have three options to reshuffle their back line.

Christian Lealiifano could move to flyhalf with either Joseph Tomane or Pat McCabe slotting in at inside centre, or rookie Zack Holmes could be thrown in the Super Rugby deep end in the No.10 jersey.

The Brumbies could also draft in club rugby scrumhalf Beau Mokotupu to training this week as cover for Nic White. An exhausted White lasted 30 minutes against the Cheetahs before his battle with the flu took its toll.

The young Brumbies will take on a formidable Chiefs back line which includes All Blacks Sonny Bill Williams, Aaron Cruden and Richard Kahui, as well as rising stars Robbie Robinson and Tim Nanai-Williams.

''The Chiefs have a star-studded back line and it's a massive challenge for us,'' Larkham said.

''It will be the best back line we've come up against, so it's going to be a big for us. We've had our combinations for six months and now it's starting to transfer into games.

''You would like to win by four tries and big margins, but the fact we're winning these tight games is massive and very promising.

''[Toomua] played well and the combination between Matt, Christian [Lealiifano] and Andrew Smith was outstanding and we'll wait to see how Matt pulls up before making a decision.''

The Brumbies fly to New Zealand on Wednesday and the coaches will meet this morning to start selecting their touring squad.

While they wait for Toomua's scans, scrumhalf White will be given a chance to recuperate in the hope he recovers from his illness.

Robbie Coleman was going to be used as the Brumbies' third-choice scrumhalf, but it is still uncertain when he will return from his groin injury.

Tuggeranong Vikings captain Mokotupu was at Brumbies training last week and will start joining in drills this week to be prepared for a late call-up.

White's absence opened the door for Ian Prior to stake his claim for the No. 9 jersey.

Prior's 50 minutes of action was the most time he had spent on the field in a Super Rugby game.

He earned six caps as Will Genia's back-up at the Queensland Reds last year, but also spent time on the wing.

''Whitey was getting better, so I didn't know what was going and I had to wait for my chance and it came earlier than expected,'' Prior said.

''We were warming up and the physio came screaming over … I played 40 minutes on the wing for the Reds last year but that was the most I had played at halfback [in Super Rugby]. ''It was nice to get a feel for the game and make my way into the game which is what I felt I did.''