Porplyzia, who kicked two goals against the Western Bulldogs only last week, will now prepare for shoulder surgery as soon as Monday.
Coach Neil Craig said the decision was made in consultation with Porplyzia on Wednesday afternoon.
“The bottom line is that the state of the shoulder is a bit different to how it was for most of the season – it’s looser and more likely to come out,” Craig told afc.com.au.
“He can play but there are now more situations where he is limited in what he can do. It came back to his ability to perform and the risk of going into an elimination final and possibly being a player down.
“Jason did a great job for us last week. He’s been great for us all season and helped us into the finals.
“He set a great example for the playing group with his desire to play and perform.”
Versatile big man Brad Moran has replaced Porplyzia in the line-up, which means the Crows will head into Saturday’s knockout clash with a three-pronged attack of talls.
Football operations manager John Reid said the match committee thought the forecast weather conditions would be conducive to playing Moran with Kurt Tippett and Ivan Maric.
“We feel that Brad has got a variety of positions he can play,” Reid told Radio 5AA.
“We think he can give us something in the forward line, he can be involved in the ruck, he can also play back and we’ve found that he can play back on either a tall or a medium-sized player.
“I know Neil’s been pretty keen to play all three talls and the weather this weekend looks like it’s going to be fine, so we’ll see how that one goes.”
