David Pocock will miss this summer's Test series against the Lions after rupturing a cruciate ligament.
The Australia flanker was injured while playing for the Brumbies in Saturday's Super Rugby action, and scans have confirmed serious damage to his knee.
Pocock will miss the rest of the season, depriving Wallabies coach Robbie Deans of a No 7 whose recent form has drawn comparisons with New Zealand great Richie McCaw.
"To hurt my knee so early in the season is obviously disappointing," Pocock said.
"The medical staff have given me plenty of time to make a full recovery so my focus has to turn to making that a reality.
"We had 17 different surgeries during the off-season so I've got faith in the club to get me back to full strength."
Pocock's Brumbies team-mate George Smith could rival Waratahs back-rower Michael Hooper and Liam Gill of the Reds for Pocock's Lions place.