Toomua missed last week's 33-20 win against the Western Force with an ankle injury, while Speight rolled his ankle in the same game before coming off midway through the second half.

The Brumbies have booked a place in the finals, but can finish as high as second on the table if they beat the Crusaders and the NSW Waratahs slip up against the Queensland Reds.

Brumbies scrumhalf Nic White said coach Stephen Larkham would most likely play Toomua at inside centre to keep Christian Lealiifano at flyhalf.

"He'll probably go the same as the Lions [game] - leave [Lealiifano] at 10 and [Toomua] at 12, but they interchange so well," White said.

"[Speight] did some change of direction and I assume he'll have right up until Saturday to prove his fitness.

"We've got good depth, but both of those guys are world class and having them is a huge boost."

The Brumbies are level with the Waratahs on 47 points, but have one win less this season than NSW.

That places more emphasis on winning with a bonus point, especially since the Waratahs will be favoured to defeat the Reds at Allianz Stadium on Saturday night.

White said the Brumbies have learnt their lessons from past years.

"We're trying not to go in our shell at the pointy end of the season," White said.

"The last couple of years we've been guilty of going into our shell in these big games, so it's about going out there and expressing ourselves.

"We're playing finals regardless, so you can go out there with a bit of confidence knowing that [with] a loss [we are] still going to come sixth."

The Crusaders are in the unusual position of being out of finals contention, but will be a dangerous opponent as they look to send off departing greats Richie McCaw and Dan Carter in style.

"They like to hold a lot of width and play, so it's going to be an open game," White said.

"They're going to chance their hand against anyone, no matter what time of season.

"But they might have something funky in there since they can't make finals."

Along with the chance to secure an all-important home semi-final, the Brumbies will be looking to celebrate captain Stephen Moore's 100th game for the club.

Moore will bring up his century for the Brumbies after making the move from the Queensland Reds at the start of 2009.

The 32-year-old Wallabies veteran said the milestone was the furthest thing from his mind heading into such a big game.

"Those personal achievements are good I guess, but the focus is squarely on the team's success," Moore said.

"You look at the AFL and the [English] Premier League; guys are racking up 600, 700 games there, guys like Steven Gerrard, who's a hero of mine.

"Nothing's out of reach, I guess."

SATURDAY: ACT Brumbies v Canterbury Crusaders at Canberra Stadium, 3.30pm. Live on Fox Sports. Tickets available from Ticketek.