If the coach gives him the nod, the next few weeks may well define the early rugby career of stand-in Wallaby No 10 Berrick Barnes.

With news that regular pivot Stephen Larkham is now in doubt for the rest of the Rugby World Cup after undergoing a second knee operation, Barnes may end up running the cutter for the Australian side during the remainder of the tournament.

That prospect looms as a huge challenge for the 21-year-old, given that if all predicted results fall into place – he will line up in consecutive weeks against Jonny Wilkinson and Dan Carter in the quarter- and semifinal.

“You would have to say Berrick would be favourite to start at this stage, but we do have a couple of options so we’ll sit down and discuss that after the (Canada) game on Sunday,” coach John Connolly said.

Barnes has been rested for this weekend with Julian Huxley handed a start in the 10 jersey. Larkham may still be available for the semifinal but it will be a race against time to have his knee cleared up by that stage.

“I’ve spoken to the medical staff and they really can’t say when he’ll be fit to play,” Connolly said. “He’s very disappointed, obviously, because he was coming along quite well. He’s one of our most experienced players and very much in our plans.