Brumbies coach Stephen Larkham has no doubts Christian Lealiifano will step up in Matt Toomua’s absence in their must-win match against the Waratahs.

Brumbies coach Stephen Larkham is backing Christian Lealiifano to rediscover the scintillating Super Rugby form that earned him last year’s Wallabies debut when he returns to the playmaker role against the NSW Waratahs.

Having undergone ankle surgery in December, Lealiifano has battled to find the x-factor that earned him 13 caps for the Wallabies in 2013.

But that could be about to change, with Matt Toomua’s groin injury giving Lealiifano another crack at his preferred role at No.10 when they travel to ANZ Stadium on Saturday night.

It’s a position Lealiifano excelled in while Toomua was injured in 2012, launching himself on to the Wallabies’ radar with more than half-a-dozen man-of-the-match performances.

“He loves playing at 10, it’s probably his favourite position. So he’s really looking forward to the opportunity,” Larkham said.

Larkham admitted Lealiifano will have “a fair bit on his plate”, however, as the backline has been shuffled numerous times throughout the week.

Toomua was only ruled out of the clash late on Tuesday night, while utility Robbie Coleman is on standby to play at inside centre with Andrew Smith battling a hamstring concern.

“So it’s going to be a very difficult game for him in terms of organising the team,” Larkham said.

The forward pack is in an equal amount of disarray, with fourth choice hooker Ruaidhri Murphy given first crack at filling injured stalwart Stephen Moore’s No.2 jersey.

Having never played a professional game at hooker in his life, the born and raised Irish prop will face a huge challenge when he locks horns against the Waratahs’ all-Wallabies front row.

“It’s a tough ask, but Ruaidhri’s a very solid human,” Larkham said.

With Wallabies lock Sam Carter also injured in the first Test against France, Leon Power will pack down next to Scott Fardy.

It’s a must-win match for the Brumbies, as a loss will end their chances of topping the Australian conference.

Their woes haven’t prevented the Waratahs from angling for the underdog status, which brought a smirk to Larkham’s face.

“That’s interesting. They’re playing at home with more Wallabies than anyone else in Australian rugby,” he replied.

Meanwhile, in a rare slice of good news, Wallabies winger Joe Tomane has killed off speculation he was set to join the Queensland Reds by re-signing with the Brumbies until the end of 2016.

“Working under Stephen Larkham has been a highlight for me,” he said.

“This is the best place for me to become a better player.”

Brumbies: Jesse Mogg, Henry Speight, Tevita Kuridrani, Andrew Smith, Robbie Coleman, Christian Lealiifano, Nic White, Ben Mowen (capt), Jarrad Butler, Jordan Smiler, Leon Power, Scott Fardy, Ben Alexander, Ruaidhri Murphy, Scott Sio. Res: Luke Holmes, Ruan Smith, JP Smith, Fotu Auelua, Jack Whetton, Michael Dowsett, Clyde Rathbone, Lionel Cronje.