Warner is being closely monitored after hurting his neck in a fielding drill just two days before the Gabba Test, sending a scare through the Australian camp.
Warner has been having treatment for a neck strain, while Marsh has had back trouble, with all-rounder Glenn Maxwell placed on standby.
Marsh has played in nine out of 10 IPLs, only missing the second season of the tournament in 2009, but at 34 his presence in 2018 can not be taken for granted. But Marsh himself being under a cloud muddies those waters somewhat.
Australia captain Steve Smith said Warner's prognosis was positive.
Smith said he would have batted first if he won the toss and said his team was excited to get the series going. "He's very confident and he says he'll be right to go", ESPNcricinfo quoted Smith, as saying.
He previously played T20 cricket for Glamorgan in 2012, and spent part of 2017 with Yorkshire. "Guys have injuries every now and then, and have little niggles". "He said he'll even bat like Shivnarine Chanderpaul if he has to, and face the other way".
"These sort of things tend to crop up before a big series but I don't think we need to change our plans on anything".
Should Warner feel stiff on Thursday morning, Maxwell will be thrown a lifeline and be recalled into the side, leaving the door open for Cameron Bancroft to form a West Australian partnership with Shaun Marsh.
However, Maxwell has played Australia's four most recent Test matches, in India and Bangladesh, and also scored a 100 in Ranchi in March.
However, he is yet to play a Test match on home soil, and was overlooked in the original squad as the selectors instead opted for Marsh as the No. 6 batsman.