Gawn and teammate Jack Viney collided early in the first quarter at the Gabba and the ruckman initially ran away from the contest.
But the influential Demons' skipper was no sooner running to the sideline and, after being subbed out, struck a forlorn figure as he sat on the floor of the dressing room with his left knee wrapped in ice.
Melbourne performance manager Alan Richardson didn't rule out an ACL tear in a mid-game interview with the Seven Network.
He referenced the vision of a devastated-looking Gawn but played down its significance, insisting the medical staff remained hopeful the injury was not that serious.
Gawn suffered a grade two medial ligament sprain to the same knee in 2020 and missed six weeks.
Steven May had already been scratched for the Gabba clash, the key defender unable to get up for what was to be his return from a hamstring injury.
And earlier on Friday the club confirmed Christian Salem has suffered another setback, with the defender's AFL return further delayed by a knee injury.
Salem, who was sidelined for more than two months last year because of a separate knee injury, had been on the verge of making a comeback after battling a thyroid issue.
The 27-year-old speedster was considered available for selection this week and had been earmarked to play in Casey's VFL match against Footscray.
But he was sent for scans on Friday after experiencing soreness in his left knee and has been ruled out indefinitely.
"He experienced some soreness following the main training session earlier in the week and scans have today revealed a small tear in his meniscus," Richardson said.
"We are still gathering further information and will be in a better position next week to understand what his rehabilitation program looks like."
Salem was grounded in February by illness related to his thyroid gland, and had battled a similar issue in the past.
The illness impacted his heart rate, blood pressure, body temperature and weight.
The 143-game defender lost six kilograms due to the thyroid issue soon after being drafted in late 2013.
And in 2016, his resting heart rate at one stage rocketed to around three times the normal level.
Salem played 13 games last year, including both finals as the Demons exited the premiership race with defeats to Sydney and Brisbane.
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