A goliath who has played 19 games this year with little support in the ruck, Grundy will be on parental leave during Saturday's match at the SCG.
Grundy's absence has created an opening for towering ruckman Will Green to finally make his debut, almost three years after he was drafted.
Pick 16 in the 2023 draft, Green has started to thrive in the VFL and is coming off recording 41 hit-outs against GWS in the Swans' last match.
"What the players love about you (Green) is your ability to compete, your mobility and your ability to play your role," head coach Dean Cox said in a Swans meeting on Friday.
"That's something you've done in the VFL so take real confidence doing it again."
The Swans secured a narrow win over the Power in Adelaide less than two months ago.
But Port have traditionally proven a tricky opponent for Sydney, who are trying to consolidate their top-two spot amid a late challenge from Hawthorn.
Port will also blood a debutant with mid-season draftee Alex van Wyk coming in due to key forward Mitch Georgiades battling a virus.
Lachie Jones is also a late withdrawal with Jacob Wehr coming into the Power's 23.
Injuries have hit Port hard during Josh Carr's first season as coach since taking over from Ken Hinkley.
Superstar Zak Butters (ankle) is attempting to get back before the end of the season for what looms as a farewell game before an expected trade to a Victorian club in October.
Butters desperately wants to play again this season despite Port (6-14) being out of contention for a wildcard spot.
"We're not just going to put Zak out there if we feel like he's at risk of hurting himself again," Carr told reporters in Adelaide on Friday.
"He's made some massive progress in that ankle.
"It's still a while away.
"More likely the last game than next week, but there's still a lot of water to go under the bridge."
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