Wallaby No 8 David Lyons has been ruled out of the World Cup after fracturing his left leg in the Wallabies' 37-6 win over Canada on Saturday.

Lyons fell awkwardly in the second half and was assisted from the field before being sent for x-rays which confirmed a fractured fibula.

"The normal recovery period for a fractured fibula is between three and four months," said Australia team doctor Martin Raftery.

"It would certainly be impossible for him to return to play during the World Cup."

The Wallabies are likely to send for a replacement before next weekend's quarter-final against England.

Loose forward Jone Tawake, veteran Matt Cockbain and lock James Horwill were all on the Wallabies' stand-by list.

Australia currently has Stephen Larkham (knee), Stirling Mortlock (shoulder) and Scott Staniforth (shoulder) all sidelined.

"We haven't yet thought about a replacement but we do have the option to bring someone else across, and we will consider that over the next 24 hours or so," said Australia coach John Connolly.

Lyons was making his first test appearance since coming off the bench against South Africa in the Tri Nations on July 7.

He was ruled out of the Tri Nations and Bledisloe Cup decider against New Zealand in Auckland after suffering deep vein thrombosis and has been on blood-thinning medication ever since.