Monfries withdrew from the Power’s Tuesday training session with hamstring tightness and underwent scans on Thursday to assess the problem.
No replacement has been confirmed at this stage, with Sam Gray, Tom Logan, Jake Neade and Ben Newton named on the Power's extended bench for the game along with Hamish Hartlett, Jarman Impey and Dom Cassisi.
That extended bench will be whittled down to four players and revealed first on portadelaidefc.com.au on Friday afternoon at 4:30pm.
Meanwhile, Andrew Moore and Paul Stewart will make their returns from injury via the SANFL, after being named in the Magpies squad to take on North Adelaide at Alberton Oval on Saturday.
Irish recruit Daniel Flynn will also make his anticipated return from a two-game rough conduct suspension with the Magpies.
South Australian Under-18 team captain Jake Johansen may also play his first League game for the year against the Roosters, with Ben Haren, Zac Hawkins and Ben Sawford also named on an extended bench.
Port Adelaide play the Roosters at Alberton Oval at 2:10pm on Saturday 12 July ahead of the club's away AFL clash with the Tigers at Etihad Stadium on Sunday 13 July at 1:10pm (AEST).
Port Adelaide Round 17 team v Richmond
FB: Cam O’Shea, Jack Hombsch, Tom Logan
HB: Matthew Broadbent, Tom Jonas, Jasper Pittard
C: Jared Polec, Travis Boak, Kane Cornes
HF: Sam Gray, Justin Westhoff, Matt White
FF: Robbie Gray, Jay Schulz, Chad Wingard
Foll: Matthew Lobbe, Ollie Wines, Brad Ebert
Interchange from: Hamish Hartlett, Jarman Impey, Jake Neade, Kane Mitchell, Ben Newton, Aaron Young, Dom Cassisi
In: S. Gray, Logan, Neade, Newton
Out: Monfries (hamstring)
Milestones if selected: Justin Westhoff – 150th AFL Game, Cam O’Shea – 50th AFL Game
Port Adelaide Round 17 SANFL team v North Adelaide
FB: Nathan Krakouer, Tom Clurey, Daniel Flynn
HB: Henry Slattery, Lewis Stevenson, Anthony Biemans
C: Andrew Moore, Steven Summerton, Karl Amon
HF: Darcy Byrne-Jones, John Butcher, Sam Russell
FF: Brendon Ah Chee, Mitch Harvey, Mason Shaw
Foll: Angus Bruggemann, Paul Stewart, Robbie Young
Interchange from: Ben Haren, Jake Johansen, Danny Butcher, Zac Hawkins, Ben Sawford
In: Johansen, Stewart, Moore, Flynn, Haren, Hawkins, Sawford
Out: Logan, A. Young, O’Shea, Newton, Neade (AFL)
Milestones: Steven Summerton - 150 SANFL game
Port Adelaide Round 17 Academy team v North Adelaide
FB: Tom Corcoran, Harris Jessen, Keenan Ramsey
HB: Tom Gray, Jackson Williams, Matt Venter
C: Justin Mills, Jack Cooper, Brad Coulson
HF: Sean Davidson, Sidney Masters, Anthony Prior
FF: Declan Hamilton, Sam Gordon, Jake Haarsma
Foll: Jonathan Ross, Matthew Williams, Louis Sharrad
Interchange from: Rivva Karpany, Levi Proude, Keanu Miller
