The Brumbies star, who missed out on a Wallaby cap last season following an horrific ankle injury, was stretchered off after attempting to tackle opposite man Jonathan Davies moments after the series kicked off at the Suncorp Stadium.
Lealiifano was replaced by the more experienced McCabe in Brisbane but the former vice captain suffered a similar fate just seven minutes after half time. McCabe took a knock to his neck and, having fractured his neck in November, definitely won't be fit for this Saturday.
The 25-year-old hasn't yet been ruled out of the third Test in Sydney, however, with the Qantas Wallabies waiting for a further assessment before making an announcement on his long-term diagnosis.
Berrick Barnes is another awaiting assessment on the head injury he picked up towards the end of the first period at the weekend but the Australian management are hopeful that Digby Ioane and Adam Ashley Cooper will have recovered from shoulder problems to take their places in the starting line up on Saturday.
"They're expecting Christian will be fine and they're hopeful with Digby and Adam that, with a bit of rehab, they can be back," said a Qantas Wallabies spokesperson.
"(Lealiifano) passed the concussion test on the night, so he was actually keen to come back on, but the time had expired.
"Pat McCabe won't be available this week ... We may know more about the significance of (it), whether he's just irritated it or there's something new there."
Meanwhile, veteran flanker George Smith insists he is more than up for the challenge of facing the Lions for a second time some 12 years after he starred in the last series in Australia.
The 32-year-old won the man-of-the-match award when the Wallabies clinched the 2001 series and is now in line to attempt to repeat the feat having recovered from the knee injury that prevented his selection for the original squad earlier this month.
"I'm ready to go. There's no confusion about my fitness or my knee injury or what not because it's not existent any more, in my mind. And mentally I definitely feel refreshed," said Smith.
"Coming off a Japanese Top League season and then into the Super Rugby championship, the five weeks off has definitely been a blessing in disguise. It's allowed me to concentrate on areas that I was lacking, whether it was my fitness or niggling injuries I had.
"My determination and passion for the Wallabies hasn't changed. There's a huge job for the Wallabies to do this weekend and whatever involvement I have, whether it be on the field or off the field, I'm happy to contribute."