Former Wallabies playmaker Elton Flatley believes Robbie Deans is unlikely to find room for both ex-vice-captains Berrick Barnes and Matt Giteau in Australia's 30-man Rugby World Cup squad.

Adding further significance to Barnes' eagerly-awaited comeback this weekend from footballers' migraine, Flatley says three doesn't go into two, leaving only one of the ball-playing midfielders to join star five-eighth Quade Cooper on the plane to New Zealand in September.

"So Robbie might have to make a decision on that. That's his job," Flatley told AAP on Wednesday.

"But if you had to, you probably wouldn't go with three - obviously Quade is the first-choice 10 at the moment and Berrick and Gits probably cover the same positions - 10 and 12."

With coach Deans preferring hard-running inside centres Pat McCabe and reserve Anthony Faingaa ahead of Giteau for Saturday night's Tri Nations opener with South Africa, Wallabies teammates on Wednesday rallied around the relegated 92-Test veteran.

Flatley agreed with hooker Stephen Moore and lock James Horwill that Giteau had been harshly judged following Australia's embarrassing 32-23 loss to Samoa on Sunday.

"I still think Gits is a world-class player," he said.

"He was behind a pack that just got physically dominated. So it's never easy for a five-eighth when that's the case.

"Gits has still got a lot to offer the Wallabies this year."

But with Deans offering the 28-year-old no guarantees, Barnes has a golden opportunity to press his World Cup claims when he lines up for Sydney University against Penrith on Saturday.

He hasn't played for five weeks but Flatley - who had to prematurely retire at just 28 after his own series of head knocks - has been in contact with his former Queensland Reds teammate to offer support and advice.

"It doesn't matter from what injury, you might have a few reservations," Flatley said.

"But Berrick's a smart guy so he knows how his body is and he'sgetting good medical advice.

"I don't think it should be a huge thing for him. Coming back in a club game, he can feel his way back into it. He doesn't have to come out and play his best game of footy.

"He just has to get in there and do some good things, go and have some fun.

"Bring the smile back, don't worry about it too much and just get out there and play.

"We all want to see Berrick back out there and running around and playing some good footy and, hopefully down the track, it's a World Cup year and we'll be looking at him playing some good footy.

"I know Berrick's goal is to play in that World Cup."

While Barnes opted to take time out after enduring painful headaches during several games in the Super Rugby season, Flatley said the series of concussions that forced him to hang up the boots were "a different situation".

"I basically got to the stage where, if I got a hit, there was a bit of a blurred vision," he said.

"It would come on quickly and go away pretty quickly but, playing five-eighth, you can't have that.

"When it started happening more and more, I just knew that it wasn't right and then I started to shy away from contact situations a little bit and, as soon as you start doing that, you're nowhere playing professional rugby.

"I don't know all the ins and outs of Berrick's situation and hopefully it will never come to that.

"Hopefully he's got a very long career ahead of him."

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