Stewart was substituted out of Geelong's thumping round 24 win over West Coast with hamstring tightness but coach Chris Scott had maintained he would be fit for Thursday night's blockbuster.
But news broke on Thursday evening that Stewart, one of the league's best defenders who has shifted into the midfield with great success this year, had failed to overcome the injury.
It opens the door for one of Sam De Koning, Gary Rohan and Oisin Mullin, who have been named as emergencies.
Geelong were contacted for comment. Port Adelaide assistant coach Hamish Hartlett told SEN that Stewart's absence wouldn't change any planning from their perspective.
Stewart's expected withdrawal came after Port Adelaide coach Ken Hinkley stressed he was determined not to be fooled by the trickery of his Geelong counterpart Scott.
Hinkley knows Scott will delve deep into his savvy strategies when Port host the Cats at Adelaide Oval.
Scott is a modern master of AFL coaching, renowned for shrewd tactics that can mess with a rival's plans.
He also has a reputation for swinging late changes.Â
"We would rather play our game," Hinkley said ahead of the opening fixture of the AFL finals.
"If you watch them play, they do have a lot of tricks that they throw around at you.
"So we're going to make sure we do our best and not get distracted by it."
Top Cat Chris Scott is renowned as a master of modern coaching. (Joel Carrett/AAP PHOTOS)
Scott is the most experienced coach in these AFL finals with 13 wins, 15 losses and two premierships.
The top Cat has an 11-4 win-loss record against Hinkley, but the Power coach has won the past two clashes in the play-offs, in the 2021 and 2020 qualifying finals.
Hinkley had insisted he wasn't fazed how Geelong had planned to use Stewart or roaming star forward Jeremy Cameron.
"We don't singularly worry too much about any individual," said the 57-year-old, who has won five of his dozen finals as Power coach.
"We can't afford to do that because Geelong have got great flexibility in their team, they throw them around everywhere.
"So we won't go in there worrying too much around what their players will and won't do.
"We will have plans in place for certain parts of our game that we need to make sure we're right, and if that involves some of their players, we will take care of that.
"We can't determine where Geelong put their players. We have just got to put our players in the right spot."
Port recalled Charlie Dixon - he missed the last minor-round game because of illness - and Quinton Narkle to replace half-back Kane Farrell (hamstring) and ruckman Dante Visentini, who was dropped.
