The Wallabies winger pulled up in the second half of their 68-22 victory in Nelson today and could potentially be replaced in the squad by Lachie Turner.
Australian coach Robbie Deans confirmed Mitchell would not take any further part in the tournament.
"We picked up another [injury] tonight. Obviously Drew Mitchell, which doesn't look good; looks like it will end his tournament. So that's unfortunate for him and us,'' Deans said.
Skipper James Horwill said it had been tough to see Mitchell go down again, after he had batted back from other ailments this year to make the Cup squad.
"Obviously we are all disappointed for him and he's been through a tough time this year with injuries so hopefully it's the last of it for him,'' Horwill said.
With the quarter-finals looming, Deans may have hoped his side were given a tougher workout in their final pool game but he was upbeat after the match.
"To be honest right now we are looking ahead. We got out of the game what we sought. We've qualified for the play-offs. Clearly we'll have to sit and watch and wait to see who we are playing against. But it appears most likely it'll be South Africa and we'll just push on from here. So it's a different circumstance from this week and it's something that we are very excited about.''
Injured outsides Kurtley Beale and Digby Ioane are expected to return next week, which was a relief to Deans.
The game itself was never going to be close and Australia racked up 10 tries in all, including doubles for David Pocock, Berrick Barnes and Mitchell.
Second-five Barnes opened the scoring after only eight minutes when he took a sharp pass from Quade Cooper and cut through the Bears to dot down and that effectively began the procession.
As was often the case, Cooper had a hand in many of his side's five-pointers and his running game, vision and pace was all too much for a valiant Russian outfit.
Although, Cooper will no doubt cop more criticism from people in New Zealand after he threw an intercept pass to Russian winger Denis Simplikevich and the 20-year-old scooted away for a try.
Seemingly every time Cooper touched the ball he was booed by the crowd.
There was plenty of hype surrounding Radike Samo's shock move to the right wing, but the transplanted No 8 hardly set the world alight with his performance, although he did produce a couple of big runs.
For their troubles, Russia, the 21st ranked team in the world, managed the odd strong spell and the crowd burst in to life when winger Vladimir Ostroushko scored in the first half.
Patchy rain in the second spell halted the Wallabies' progress at times, but the speed with which they moved the ball was a level far and above Russia's capability.
Another bright spot was the goal-kicking of precocious fullback James O'Connor, who slotted nine goals from 10 attempts.
In one of the more bizarre scenes of the tournament, replacement pivot Konstantin Rachkov set himself and banged over a drop goal, with his side down 54-5 on the scoreboard.
Other than slightly improving their points differential it certainly wasn't going to put them in a spot to win the game.
Rachkov also put his name in the try-scorers' column when he crossed the chalk in the 69th minute, again to the delight of the noisy Nelson crowd.
Australia 68 (Drew Mitchell 2, David Pocock 2, Berrick Barnes 2, Ben McCalman, Stephen Moore, Adam Ashley-Cooper, Salesi Ma'afu tries; James O'Connor 9 cons) Russia 22 (Vladimir Ostroushko, Konstantin Rachkov tries; Rachkov 2 cons, drop goal) HT: 47-5