Barnes rolled his ankle at training yesterday and an MRI scan has revealed the 23-year-old has suffered a tear of the syndesmosis ligaments in his left ankle.

He had already been ruled out of tomorrow’s Bledisloe Cup clash against New Zealand but the injury is likely to require surgery and will sideline Barnes for several months at least.

Australia Under-20 fly-half Matt Toomua now comes into the Wallabies' squad as full replacement for Barnes after initially being called up as cover for the young playmaker for next week's tour match against Guinness Premiership club Gloucester.

The 19-year-old Toomua left Sydney for London last night, and will join the Wallabies touring party when the team arrives in the United Kingdom on Sunday to begin their six-match tour.

Toomua has become the second member of the Brumbies to be added to the touring party this week, after midfield back Tyrone Smith was added to the group as replacement for NSW Waratahs back Rob Horne, who tore his hamstring at training.

Toomua represented his country at the Under-20 World Cup in Japan earlier in the year and is just back from a short stint playing for Western Province in South Africa's Currie Cup provincial competition.

Australia face England on November 7, Ireland on November 15, Scotland on November 21 and Wales on November 28.