The hard-hitting centre was taken off in the 15th minute following a knock from behind while he had his head down.
Larkham said he was unsure how long McCabe, a veteran of 20 Tests, would be out of action.
"We'll have to be very careful. Concussions are very serious. We'll follow the protocols and make a decision,'' Larkham said.
"But he had a strong 15 minutes, carried the ball well and made a couple of breaks.''
The Brumbies may have scored the only try in their first hit out of the season, but five penalties to the Highlanders proved enough to get the home side across the line.
Larkham said he was pleased with the performance, in what was his first game holding the reins since World Cup winning coach Jake White departed the club last season.
"They kicked five penalties to win the game, so we're happy that our defence held out,'' Larkham said.
The Brumbies jagged a slender 11-9 lead right on half time, courtesy of an unconverted try to Sam Carter and two penalty goals to new South African recruit Lionel Cronje.
However, it would be the last points the visitors scored, with the Highlanders kicking a penalty goal in each of the final two quarters - the last of which was on the back of a yellow card to Brumbies back Andrew Smith.
While the match was second versus second last from last year's 2013 season, Larkham had elected to rest all members of the Wallabies' Spring Tour squad, as well as only playing his strongest side in the first half.
- AAP