Ryder has been a key recruit for the Saints since joining the club ahead of the 2020 season, with he and Marshall playing vital roles in St Kilda's finals finish last year.
The 33-year-old is nearing the end of his career, prompting Montagna to suggest the Saints should use this year's exchange period to add experienced ruck talent instead of draft prospects as their premiership window nears.
“They need to go and try and get one from another club – getting an 18-year old ruck won’t help them in the next window,” Montagna said on Fox Footy.
The St Kilda great named a trio of senior Greater Western Sydney ruckman - who could consider greater opportunities elsewhere - as potential targets, as well as Magpies youngster Max Lynch, who was linked to an exit from Collingwood this week.
“There are always young rucks that are not getting a game at other clubs. GWS have got three – Braydon Preuss to come back, there’s either (Kieren) Briggs or (Matthew) Flynn. We hear Max Lynch from Collingwood may be on the market.
“Clubs have had success getting a young ruck that hasn’t been getting a game at one club and turning them into a very good ruckman.
“They’ll need to try and find someone to compliment with Rowan Marshall going forward.”
The Saints are tipped to have a large space in their salary at season's end, with Jack Billings, Jake Carlisle, Luke Dunstan, Seb Ross and James Frawley among a host of players unsigned past this season.