The Brumbies and the Wallabies have suffered a heavy blow as David Pocock will be out of rugby for six months.
Pocock was injured playing for the Brumbies and scans have now confirmed that he has torn anterior cruciate ligament (ACL) and will be out of action for at least six months.
Pocock suffered the injury when he fell awkwardly in a tackle by fellow Wallaby Adam Ashley-Cooper who was playing for the Waratahs.
Former Wallaby captain Pocock now faces a knee reconstruction and is expected to miss the rest of the Super Rugby season as well as the British and Irish Lions tour and the Rugby Championship.
Pocock was in contention to be coach Robbie Deans' choice to skipper the Wallabies this year.
Injuries last year forced Deans to switch the captaincy from James Horwill to Pocock before he injured his right knee.
Deans will now have to find a flanker replacement for Pocock with the early contenders likely to be the Waratahs' Michael Hooper or Liam Gill of the Queensland Reds.
Wallabies great George Smith, a veteran of 110 Tests, could also emerge as a contender after replacing the injured Pocock in Saturday's match.
However, Smith's Test availability is not clear as he is still contracted to a Japanese club and only playing for the Brumbies on a short-term deal in the Japanese off-season.
Brumbies captain Ben Mowen said the loss of Pocock was a big blow.
"You invest a lot in your playing group and the friendships that you build and you really do ride the highs and lows with each other," Mowen said.
"But in saying that, he's an absolute quality guy and if anyone's going to do the recovery right ... he's going to be the guy who's going to do it."
Brumbies coach Jake White said it was fortunate that the Brumbies had recently signed Smith to play most of this year's Super Rugby tournament.
"It shows you how fate plays out ... it's just fantastic how things have worked out now that George has arrived," White said.
"It's not nice on Poey (Pocock), but at the same time it just shows how important depth is in this competition and when you have depth like George it's even better."