The Demons failed in their bid to have van Rooyen's three-game ban for striking overturned or reduced.
It means he will miss the fifth-placed Demons' final home-and-away game on Saturday against the Western Bulldogs, and that Melbourne will need to win two finals for him to play again this season.
Van Rooyen is having a career-best season, kicking 42 goals in 22 games.
The Demons forward was charged with striking after he concussed Port Adelaide defender Aliir Aliir in a marking contest on Saturday night at Adelaide Oval. It was graded as severe impact, careless conduct and high impact.
After the 90-minute hearing, where van Rooyen testified that he was trying to mark the ball when he collected Aliir, the tribunal jury deliberated for nearly an hour before upholding the charge.
Melbourne had argued van Rooyen's attempt to mark the ball was not careless, but the tribunal rejected their case.
Tribunal chair Jeff Gleeson KC also turned down a bid from the Demons to have a biomechanist give evidence for van Rooyen.
"The swing of Van Rooyen's left arm constituted the act of a strike. It was a forceful blow. It was not simply a trailing or leading arm that Aliir collided with," Gleeson said in the verdict, adding the panel found it was careless.
"Van Rooyen was initially intending to mark the ball, but we find that shortly before impact, he ceased to intend to mark the ball. We say this despite van Rooyen's evidence to the contrary.
"Even if it was van Rooyen's sole objective at all times to contest the mark, we find that he did so in a way that failed to take reasonable care to avoid acts which could be reasonably foreseen to result in a reportable offence.Â
"Van Rooyen had time to move his right arm in response to seeing Aliir and he could have done so to some extent or sufficient extent with his left arm."
The tribunal also found the impact was severe and said there was potential for further injury, such as a facial fracture.
Also on Tuesday night, Brisbane AFLW key forward Dakota Davidson failed to have her one-game striking ban downgraded.
The Lions pleaded guilty and tried to argue the clash with Essendon's Maddi Gay was low rather than medium impact, but the AFLW tribunal upheld the grading.
It means one of the league's top forwards will miss the grand final rematch against two-time defending premiers North Melbourne.
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