Lealiifano will have a chance to send Wallabies coaching staff a reminder of his worth when he plays for the Barbarians invitational team against Samoa in a World Cup warm-up in London on Sunday Australian time.

The 27-year-old was one of the unluckiest players to miss out on a spot in the Wallabies' 31-man squad after guiding the Brumbies into the Super Rugby finals.

But rather than dwell on a missed opportunity, Lealiifano is determined to focus on improving his game and being a back-up if the Wallabies are hit by injuries.

Lealiifano is part of a 10-man extended squad on standby in case of injuries and he will return to Canberra next week to play for the Vikings in the National Rugby Championship.

Lealiifano is channelling his energy into being ready for Test action regardless of how unlikely a late call-up might be. "The World Cup is obviously still a goal, the fire is there," Lealiifano said.

"I feel like there's plenty more quality football left, I just have to take this as development and work on small steps to get there. You never wish injuries on anyone and hopefully everyone gets through, but the best way to approach these next couple of months is to be prepared for anything.

"This opportunity to play for the Barbarians is good for me and I'll be trying to better myself to stay ready for a chance. If it doesn't come, at least I've worked on my game."

Lealiifano is part of a 12-strong Australian contingent in a Barbarians team which also includes four World Cup winners.

The Wallabies boast playmakers Bernard Foley, Quade Cooper, Matt Toomua, Matt Giteau and Kurtley Beale in a talented World Cup rotation.

But Lealiifano has the chance to work with former New Zealand magician Carlos Spencer in Barbarians camp. "Being in and around different set-ups has been challenging, but I've enjoyed those challenges," Lealiifano said.

"Mentally it can be draining at the times with different changes, but for me it's been refreshing. To be able to keep playing footy has been enjoyable and that has been the main thing for me.

"I let the selection stuff pan out, I knew it was going to be tough to handle but I was comfortable with that. Mentally I was prepared and as hard as it is, I'm happy to move forward. I'm happy for guys like Gits and the players that are there in the squad. I'm super supportive of the squad and in a pretty good space."

Eight Brumbies were included in the World Cup squad, but Lealiifano, scrumhalf Nic White and 72-Test front-rower Ben Alexander missed out on selection.

Lealiifano and Alexander will play for the Canberra Vikings while White is preparing for his move to French club Montpellier.

Lealiifano will play alongside veteran Australian prop Benn Robinson, hooker Saia Faingaa and giant winger Taqele Naiyaravoro in the Barbarians team to show Wallabies coach Michael Cheika they're ready if needed.

They will also line up next to World Cup winners in former All Blacks Ali Williams and Adam Thomson and South Africans Bakkies Botha and Wynand Oliver.

"To have this opportunity now, I'm really excited about it and looking forward to it," Lealiifano said.

"All the tricks come out in a Barbarians game, it creates fun where [a] Test match is always finding a way to win. It has a different feel to it."