De Koning was lured to the Saints as a restricted free agent from Carlton last August on a massive eight-year deal worth about $1.7 million per season.
It cast doubt over Marshall's role at St Kilda, and the contracted big man promptly requested a trade to Geelong.
But the move was denied and Marshall returned to Moorabbin, where he insists there was no awkwardness around the off-season dealings.
"Luckily I've got a good relationship with Ross (Lyon) and all the other coaches, players and everything," Marshall said.
"At the end of the day, I'm really confident with where I am at the club at the minute.
"All I want to do is just put my head down, work hard and give everything I can to the footy club."
Marshall has spent increased time working on his forward craft in preparation for splitting ruck time with De Koning.
The pair lined up together in the season-opening defeat to Collingwood, with De Koning shouldering the bulk of ruck duties with 82 per cent of time on ground, compared to Marshall's 63 per cent.
Marshall sat out the loss to Melbourne on Sunday because of concussion but is hopeful of returning against GWS this Saturday.
"It's still a work in progress but we're really confident with the strides we made throughout the pre-season," Marshall said of the De Koning partnership.
"It's something I'm really confident will work.
"He's a great guy, Tom. He obviously works really hard and I'd met him a few times outside of footy through one of our mutual friends.
"He's a great guy and we've got a really good relationship."
After a 0-2 start, St Kilda face tough games against GWS (away) and the Brisbane Lions (home) before their bye.
"We banked a lot of tough, gruelling sessions throughout the pre-season and I'm confident we can turn it around if we get to work," Marshall said.
"It's a tough couple of opponents (coming up) but we're confident in our ability.
"If we can bring what we want to bring, we're confident that it stacks up with anybody."
Marshall was in a positive mood at a Coopers Mild promotion on Monday and is hopeful he will be given the green light to return from concussion this weekend.
"I'm going along alright so far. I've got a few more boxes to tick but so far, so good," Marshall said.
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