The hosts, 2-0 up in the five-match series, could reclaim the coveted urn in Perth and Smith said Marsh would be included, probably for Peter Handscomb, if the WACA track was not quick enough.
"We're going to have another look at the wicket in the morning and decide if we need that extra bowling option," Smith told a news conference.
"The stats suggest over the last couple of years the bowlers have had a pretty heavy workload on this wicket, so we're probably leaning that way at the moment.
"It's probably not as hard as I'd have liked it to be a day out but 24 hours can change a lot and in the morning hopefully it's a bit harder and faster."
Marsh, who had shoulder reconstruction earlier this year, would provide medium paced backup to frontline quicks Mitchell Starc, Josh Hazlewood and Pat Cummins.
Handscomb scored centuries against Pakistan in Brisbane and Sydney last season but has managed knocks of only 14, 36 and 12 in his three innings against England this year.
Smith, though, said any changes to the line-up that won the first two tests would be purely to protect the pacemen.
"If we do go down that route then it's purely because we think we need an extra bowler on this wicket, nothing to do with anyone's batting," Smith added.
"If we do go down the route of Pete missing out, it's unlucky. We still see a very bright future (for him) indeed. If he is to miss out, there's no reason he won't be back in the team soon."
Smith said he hoped the wicket would be much different from the drawn 2015 test against New Zealand when 1,672 runs were scored over five days.
"It was so evenly paced, really slow, once you got in it was almost impossible to get out," Smith recalled, adding that the groundsman had been working to get more pace into it.
"I think he's got more grass on it than he previously has to try and get that pace on the wicket."
Marsh has worked hard on his batting and would expect to slot in at number six in the order below brother Shaun, who would move up to replace Handscomb.
"I think he's tightened up his defence quite a little bit," Smith said of the younger Marsh's batting.
"In defence, he has softened his hands up a bit. He still putting away the bad ball, he hits the ball probably as hard as anyone I've seen. He's a strong lad."
(Reporting by Ian Ransom, writing by Nick Mulvenney, editing by Peter Rutherford)
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