Marshall landed awkwardly and couldn't put any weight on his right leg after competing in a ruck contest with just minutes remaining in Friday's 16.8 (104) to 11.8 (74) loss to the Dockers in Perth.
The 30-year-old had his ACL and other aspects of his knee tested by medicos on the sidelines, but Saints coach Ross Lyon is optimistic there were no concerns with Marshall's knee.
"No knee, just the shin. That's what he told me," Lyon said.
"I spoke to him, spoke to his family, as in just a casual chat, and they were like, 'No, it's just his shin', so I think he'll be fine.
"I was never overly concerned, like no one's flagged anything, although you just make me jumpy with 'was it bad?', but I don't think it was bad."
But Saints fans shouldn't be breathing easy just yet.
A week earlier, Lyon was confident Jack Higgins had only suffered grass burns to his knee rather than a serious injury in a 36-point win over Richmond.
Just days after that win, Higgins was sent in for minor knee surgery, with no exact timeline set for his return.
St Kilda were dealt a blow in the third quarter against the Dockers when Dougal Howard injured his calf, with the defender set to undergo scans to determine the extent of the strain.
Howard will join the likes of Nasiah Wanganeen-Milera (calf), Higgins (knee), Mitch Owens (calf), Max King (hamstring) and Liam Ryan (calf) on the injury list ahead of next week's clash with Hawthorn.
St Kilda led by a point early in the final quarter on Friday night as they threatened to ruin Fremantle's prospect of posting a club-record 10th straight win.
But the Dockers tore the game to shreds with a devastating six-goal burst, sinking St Kilda to a 5-6 record in the process.
One of the key match-ups in the game was Fremantle spearhead Pat Voss playing a 'keeper' type role on star St Kilda backman Callum Wilkie.
Wilkie only ended up with one intercept mark for the game, with Voss going on to kick three important goals.
Voss also ruffled Wilkie's feathers with his usual physical tactics, with the niggling kicking off right from the start of the match.
"I just thought to be honest the first 30 seconds was a bit bizarre really when there was an umpire right there," Lyon said.
"If they don't pay it, it must be within the laws and the spirit of the game, so that's OK.
"We're all big boys and we love a competitive spirit."
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