A possible season-ending knee injury to champion Wallabies flanker David Pocock has overshadowed the Brumbies' clinical 35-6 drubbing of old foes the NSW Waratahs on Saturday night.

Rated as the "premier open side flanker in the world" by his replacement George Smith, Pocock went down in the 13th minute and was assisted from the Canberra Stadium field.

If scans confirm the suspected ACL tear to Pocock's left knee, he will likely be ruled out for at least six months, missing the high-profile three-Test series against the British and Irish Lions, the Rugby Championship series and the rest of the Super Rugby season.

Wallabies great Smith didn't shy away from his earlier than expected return to the field, dominating the breakdown and showing he still has what it takes to compete at Super Rugby, and perhaps international level.

Smith said it was the physicality of the match, not his fitness, that was the major difference between the Japan league and Super Rugby.

"Obviously I'm not tackling 115kg guys in the Japan league week in, week out," he said.

Brumbies coach Jake White said it was too early to predict whether or not Pocock's season was over but conceded how fortunate it was the Brumbies had signed Smith recently to play most of the Super tournament in the off-season for his Japanese club.

"He (Pocock) is going in for a scan. These sort of players that play at this level understand when their body tells them something and he just feels it's not 100 per cent," White said.

"It shows you how fate plays out ... it's just fantastic how things have worked out now that George has arrived."

The Brumbies have not conceded a point in the second half against any team this season, a statistic Coach Jake White described as fantastic.

"We're not going to get ahead of ourselves, but at the same time it's a massive game and that's the benchmark we've set," he said.

Flying fullback Jesse Mogg was the standout for the home side as he continued to put himself in the frame for a Wallabies debut.

Christian Lealiifano got the home team off to a great start, nailing three early penalty shots and scoring a first half try to put the home side comfortably up at 21-6 at the break.

The Waratahs looked more promising early in the second half but failed to capitalise on numerous opportunities, before Brumbies winger Henry Speight crossed to put any hopes of a comeback to bed.

Mogg then set up replacement Robbie Coleman for a length of the field five-pointer in what will be a contender for try of the year and delivered the Brumbies a four try bonus point win.

Despite remaining tryless, Waratahs coach Michael Cheika said it was part of the growing pains of their new attacking style.

"We actually were playing our attacking game but our shape wasn't set up right because guys weren't getting into position quick enough," he said.

"That's why we didn't get a chance to make many breaks."

Hooker Tatafu Polota-Nau was the only injury for the Waratahs with a hamstring concern.