Rival clubs are circling St Kilda big man Rowan Marshall in what is looming as a case of ruck dominos.

With the Saints primed to land Carlton free agent Tom De Koning on a blockbuster deal worth up to $12m across seven years, Marshall is set to be relegated to second fiddle.

WATCH THE VIDEO ABOVE: Rival clubs circling St Kilda’s Rowan Marshall.

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Marshall, 29, is contracted until the end of 2027 at Saints, but 7NEWS chief AFL reporter Mitch Cleary says opposition clubs are of the belief that he would be open to exploring a move if De Koning arrives as expected.

“There are rival clubs tonight that believe if Tom De Koning arrives at Moorabbin, which looks increasingly likely as the season wears on, that Rowan Marshall will be open to exploring a trade away from the Saints,” he said on The Agenda Setters.

“Now, the Saints will hold the whip hand here. He turns 30 later this year. He has two years left on a lucrative contract at more than $800,000 a season.

“But clubs see Rowan Marshall as in play when it comes to the ruck merry-go-round at the end of the year.”

Cleary reports St Kilda are confident the two-ruck situation can work, but The Agenda Setters panellists immediately had their doubts.

Melbourne tried it with Brodie Grundy and Max Gawn, and it failed spectacularly, while the jury is out on Fremantle’s ruck pairing of Sean Darcy and Luke Jackson.

In a statement to The Agenda Setters, St Kilda coach Ross Lyon said: “I will not be brought into the pantomime around Rowan Marshall.”

Lyon holds a close relationship with Marshall, but it remains to be seen whether the ruckman will be happy to share the load alongside De Koning.

“Ross feels he’s got an extremely close relationship with Rowan Marshall. It’s even grown in the last 12 months. They regularly catch up away from the footy club and talk things outside of footy,” Cleary continued.

“Marshall’s been playing sore in the last couple of weeks with a back concern.

“The Saints are adamant that these two ruck situations are going to be working and Rowan Marshall will be brought along for the ride.

“I think there’s a bit of in-limbo from Rowan Marshall’s side of things.”

Collingwood and Carlton great Dale Thomas wondered how the split between the pair would work.

“He’s not a forward, though. So the sell is going to be, what, 50-50 ruck? Or, because as you said, De Koning doesn’t really play forward, and Marshall’s kicked six goals this year as a ruckman sometimes in that forward line. I don’t think that works with the mix they have either,” Thomas said.

Cleary explained the reasons why St Kilda think the combination can work.

“The Saints point to their low contested mark numbers this year and they feel that they’re being let down for an option down the line,” he continued.

“They feel that one of them to be playing forward will be a key option. They also point to how well Marshall played with (Paddy) Ryder as a sidekick early in his career.

“But I think this one is well and truly in play.”

Marshall and De Koning aren’t the only two rucks potentially on the move this year with Essendon free agent Sam Draper also weighing up his future.

Adelaide and Brisbane are both keen on Draper and should he land at the Crows then Reilly O’Brien, who is also a free agent, could be on the move.