Wallabies lock Sam Carter will be out of action for up to 12 weeks after suffering a torn medial ligament in the Brumbies’ Super Rugby win over the Bulls.

Scans have confirmed the worst possible news for Carter, who was forced off the field at GIO Stadium on Friday night following a sickening but accidental knock to the knee in the first half.

The prognosis means he will not only miss the Brumbies’ last two regular season matches, but also the finals if they qualify.

It also puts at risk his chances of playing at this year’s Rugby World Cup, which begins mid September.

“Like any Test player, international player, it’s going to be a loss to your team,” said club coach and Wallabies assistant Stephen Larkham on Saturday.

Carter had found some good form in recent weeks after taking time off to mourn the death of childhood friend Nicholas Tooth, only adding to the disappointment of his injury.

“He had a bit of a spell out of the game but I thought the last couple of weeks he’s really played exceptionally well,” Larkham added.

“But I think we’re lucky we’ve got good experience in the second row with Blake Enever and Rory Arnold.

“I think those guys have gained enough experience throughout the year to be able to fill the shoes Carts leaves.”

The Brumbies’ win over the Bulls – sealed with a double to winger Henry Speight – has provisionally put them atop the Australian conference, one point in front of the NSW Waratahs ahead of their clash with the Lions in Johannesburg on Sunday morning (AEST).

While a loss for the defending champions will boost the Brumbies’ chances of a finals berth, Larkham is focused on beating Western Force in Perth next Friday and the Crusaders at home the following week.

“There’s nothing we can do now,” he said.

“It’s at that stage of the season now where results are going to go your way and maybe go against you.

“The only thing you can focus on is doing your job and winning next week.

“We got four points out of (last night), which is good. Next week we’ll be happy with a win and the following week we’ll be happy with a win as well.”

Bulls coach Frans Ludeke rated the Brumbies a “huge contender” for the 2015 title, claiming they’re the best defensive outfit in the competition.

“They score a lot of tries as well, so the balance is there,” he said.

“They’ve got big-match temperament, so when the big games come up like (last night) they know how to guts it out and play it smart, play field position, use the opportunities.”