Van Rooyen was cited by the match review officer and slapped with a three-match suspension for the swinging arm that knocked out Port Adelaide's Aliir Aliir at Adelaide Oval.
As it stands, van Rooyen is banned for Saturday's game against the Western Bulldogs, plus the Demons' first two finals - or an elimination final then round one next year, depending on where they finish.
Fifth-placed Melbourne can still make the top four if they beat the Dogs and have other results go their way.
But unless the Dees successfully appeal the suspension or have it downgraded, it means bar a stunning finals run, van Rooyen's season would be over.
Van Rooyen will face the tribunal on Tuesday night in a bid to at least reduce that ban.
The incident involving Aliir was considered careless conduct, high contact and severe impact, which draws a three-match suspension.
Aliir was marking the ball in the second term of Saturday night's match when van Rooyen steamed through and attempted to spoil, but seemingly mistimed it and instead struck the defender high with a swinging arm.
The Port defender hit the ground, didn't move for several seconds and had to be helped off the field by trainers.
Aliir failed his Head Injury Assessment (HIA) test and spent the rest of his 200th AFL game watching from the bench.
Van Rooyen, 23, has kicked 42 goals and averaged 4.7 marks in his best season to date, having been rejuvenated under new coach Steven King.
He booted two majors against the Power, but will hope they aren't his final involvement for the season.
The Demons are already without veteran recruit Brody Mihocek (neck) for the remainder of the campaign.
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