Another Lions injury worry after fullback Kinghorn limps off
The Scottish star, widely seen as starter in the first Test against Australia, was limping heavily after an awkward landing early in their 36-24 win and was replaced by Marcus Smith.
Coach Andy Farrell said "hopefully it is not too serious".
"He said someone landed on his knee, he was walking around," he added to Sky Sports immediately after the match.
It is another blow for the Lions who have already lost versatile English utility back Elliot Daly to a broken arm and experienced Welsh scrum-half Tomos Williams to a pulled hamstring.
The first Test against the Wallabies is on July 19 in Brisbane.
Farrell said overall he was pleased with the performance against Australia's top Super Rugby team, but pointed to issues that still need to be ironed out.
"It was the same as the other games, there was some good stuff, especially in the first half. There was some nice, flowing attacking play that was played at a good tempo," he said.
"On the flip side, we kept them in the game. We dominated field position, but we kept them in with a sniff ... congratulations to the Brumbies, they came out of the blocks and stayed in the fight until the last minute."
The Brumbies were without eight of their top players on Australia duty, but defended stoically, while crossing for four tries.
Coach Stephen Larkham called their effort "outstanding" against what he said was "probably their Test team".
"There were a couple of lapses ... where we were just a little bit inconsistent coming out of our end, but for the majority of the game we were under the pump," he said.
"I don't know what the stats are, but it felt like we were in our half of the whole game, pretty much. And we were pretty dogged defensively.
"You know, close enough at the end of the game there. If we score a try with five minutes to go, we give ourselves a chance of winning it.
"And they were pretty good. That's probably their Test team."
The Lions play their fifth and final warm-up game before the opening Test in Adelaide on Saturday against a combined Australia-New Zealand XV.