Australia number eight David Lyons has been ruled out of the remainder of the World Cup after fracturing his left leg in the Wallabies' 37-6 win over Canada.

Lyons well awkwardly early in the second half and was helped from the field before being sent for x-rays which confirmed the fractured fibula.

"The normal recovery period for a fractured fibula is between three and four months," Australia team doctor Martin Raftery said. "It would certainly be impossible for him to return to play during the World Cup."

ACT Brumbies loose forward Jone Tawake, veteran Matt Cockbain and lock James Horwill are all on the Wallabies' stand-by list with a replacement before next weekend's quarter final against England.

Wallabies coach John Connolly said the team management had not decided on a replacement yet but were considering calling in an extra back as cover for injured flyhalf Stephen Larkham, who has already been ruled out of the quarter-final against England after undergoing two minor knee operations.

Berrick Barnes, 21, has been given the task of marking Jonny Wilkinson next weekend and Connolly said Kurtley Beale may be added to the squad as a back-up in case Larkham doesn't recover in time for the semi-finals, should Australia make it.

"It's possible [Lyons' replacement] won't be a forward but it may be an inside back," Connolly said.

"We're very hopeful that Stephen Larkham, if we progress in the tournament, can be available after the quarter-final so we'll probably bring an inside back in as a back-up to that if he doesn't make it.

"The decision to make is if you bring a 10 [flyhalf] in it would probably be Kurtley Beale but you have to ask yourself is he the one who can step into a semi-final or final if you need it? Or are you better served moving Matt Giteau in and bringing a 12 in."

Larkham has not started since the Japan game but is optimistic he will play again in the tournament.

"The knee is progressing quicker than expected, certainly I will start running some time this week," he said. The swelling has gone down and the pain has gone away."

Lyons was making his first Test appearance since coming off the bench against South Africa in the Tri-Nations on July 7 after suffering from a deep vein thrombosis and has been on blood-thinning medication ever since.

Raftery said Lyons would have to remain in France for at least another week because of complications with the medication and would probably require surgery when he returns to Australia.

"The problem we've got is the treatment for his DVT thins his blood and consequently when he sustains a fracture it makes you bleed a lot more," Raftery said.

Pippa Davis / Eurosport