Western Force coach John Mitchell has claimed the underdog status for Friday night's Super 14 clash with the Brumbies in Perth and the bookies tend to agree.

But the Force would have felt the odds turn slightly back their way after star Brumbies five-eighth Matt Giteau was ruled out on the eve of the match.

Giteau, who played three seasons at the Force before switching back to the Brumbies, has battled a quad complaint for the past fortnight but was confident of lining up against his former side.

However, the Wallaby veteran was officially ruled out on Thursday afternoon, with 20-year-old Matt Toomua to take his place in the run-on side.

"You want to be available for the first game of the season and when you've got history (with the Force) like I do, it was a match I was really keen to be a part of," Giteau said.

"But I said from the outset that I wouldn't play if my injury was going to jeopardise the performance of the team.

"As it happens, that decision has now been made and I'll now start my preparation for the Bulls.

"Matty and Christian (Lealiifano) were impressive at 10 and 12 last week.

"They've trained well again in those positions this week and they're forming a strong combination there."

Mitchell said the Brumbies, boasting a near Test-quality line-up, were the best team on paper in the competition.

"I guess we are an underdog," Mitchell said.

"You only have to look at the manner of experience in internationals that they've got within their group.

"Clearly it's a great list."

TAB Sportsbet quoted the Brumbies a $1.50 favourite against the Force ($2.50) despite the match being played at ME Bank Stadium, the Perth franchise's new home after four years at Subiaco Oval.

But Force skipper Nathan Sharpe believed the high expectations placed on the Brumbies could count against them.

"They've got some very good players on their books and one of those things is it puts a lot of pressure on them to perform," Sharpe said.

"We are not worried about what they produce, it's more what we can do to them."

Mitchell saw footage of Toomua during the pre-season and said he was aware of the young playmaker's strengths.

"He kicked well, he ran the play well, he looks confident," Mitchell said.

"He's grown even more as a player.

"If you look at the last 12 months for Matt he's had a couple of opportunities for the Brumbies in the 2009 campaign.

"He had an experience in Wellington that was pretty tough for him but he would have learnt from that situation and then he went on the Wallaby tour and also had time with Western Province, so his growth has been huge in the past year and that will hold him in good stead going into this campaign."

Wallabies prop Pek Cowan will play at hooker for the Force and Mitchell was confident the 23-year-old would be up for the role despite playing less than a handful of games in the position.

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