McInerney was helped from the field late in the first quarter at the MCG on Saturday cradling his left shoulder after it popped out.
The 30-year-old attempted to tackle Geelong midfielder Tom Atkins but hurt his shoulder in the process.
Oscar McInerney left the field after this contest.— AFL (@AFL) #AFLFinals | #AFLCatsLions pic.twitter.com/EUbjYVdIA6September 21, 2024
McInerney strapped up his shoulder and bravely played on until early in the third quarter.
But he was forced off the field again when his shoulder gave way for a second time.
During the last quarter, McInerney was taken to hospital in an ambulance for further assessment.
Lions board member Leigh Matthews, who coached the club to their premiership three-peat from 2001-03, said in commentary on 3AW that McInerney was "one player you can't replace".
Joe Daniher, the hero in the Lions' stunning come-from-behind win against GWS last week, will be forced to take on the No.1 ruck duties in McInerney's absence.
If the Lions progress to next week's grand final against Sydney, McInerney will almost certainly not be able to play.
Rather than use Daniher as the main ruck again, Brisbane would likely recall Darcy Fort, who has played just two games this year.
Conor McKenna was subbed into the match for McInerney during the third quarter.
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