The Cats, who have already landed ex-GWS skipper Toby Greene as a free agent, remain confident playmaker Gryan Miers won't be leaving for West Coast while they are in the hunt for Essendon defender Jordan Ridley.
Marshall, 30, wants to get to Geelong, having fallen behind Tom De Koning as first-choice ruckman at St Kilda, playing predominantly forward-ruck this year.
St Kilda reportedly want a first-round draft pick at a minimum for Marshall, who has a deal for next year.
"It's hard to see right now, there's some challenges to that deal, but we're committed to Rowan. We'll try and make that," Cats football boss Andrew Mackie said.
"I don't want to get into too much detail and specifics around that ... but there's work to do."
Asked if Geelong would part with their top selection, Mackie said : "No I don't think (so).
"We've been clear with them about what it looks like from our point of view - obviously the first round pick is pretty valuable, obviously pre Tasmania."
The Cats also aren't keen on offloading a player to secure Marshall.
"We're hopeful that's not needed. We feel like we've got plenty there," Mackie said.
"Pick 14 is of real value to us given what's going to transpire in the competition.
"I feel like we've got enough that we can get the trades done."
Mackie said the Cats recognised both Marshall and Ridley, who is contracted for another three years, could be held to their deals.
"We've got intentions to bring them in but we understand there is always a scenario that they're held to contract. That's real," he said.
Miers completed a medical with the Eagles before heading for an overseas holiday, in case a move eventuates.
But both the Eagles and Cats said on Monday they didn't expect him to move.
Geelong won't be fielding any offers for talented half-back Lawson Humphries, who is contracted until the end of 2028.
"We love what he does for us, and he won't be going anywhere," Mackie said.Â
Fremantle list boss David Walls also hosed down talk of a bid for Humphries.
