Marsh strained his back during training at the Gabba on Wednesday, Cricket Australia said, a day after Warner hurt his neck during a fielding drill.
All-rounder Glenn Maxwell has been drafted in as cover for Warner should the vice-captain be unable to shake off the injury.
However, there was no suggestion from the board that a second player would be brought in to cover for Marsh, who would have moved up the order to open with his uncapped Western Australia team mate Cameron Bancroft.
Australia skipper Steve Smith backed Warner to be fit and ready for the start of the five-match series, before Marsh's injury was revealed later on Wednesday.
Maxwell was omitted from the 13-man Ashes squad named last week, with Marsh named as his replacement.
The selection of the injury-prone Marsh was criticised by local media and pundits given his modest test record and Australia's usual preference for an all-rounder to help with the bowling load.
Smith said Warner's neck was causing him discomfort when lifting his head more than when he moved it from side-to-side, which could be a concern on the Gabba's typically bouncy pitch.
However, the hard-hitting lefthander eased some fears by batting in the nets late on Tuesday and told Smith he was hopeful of playing.
"Davey's confident that he'll be OK," Smith told reporters at the Gabba on Wednesday.
"He said he'll even bat like Shivnarine Chanderpaul if he has to and face the other way. So, I think he'll be alright," the captain added with a smile.
West Indies batsman Chanderpaul was renowned for his idiosyncratic front-on batting stance.
England captain Joe Root, who declined to reveal the makeup of the tourists' side, expected Warner to take his place in the home team.
"I'm sure it'll be fine, these sort of things tend to crop up before a big series," he told reporters at the Gabba. "But I don't think we need to change our plans on anything. We'll still prepare the same."
Smith also confirmed that pace trio Mitchell Starc, Pat Cummins and Josh Hazlewood will all bowl in Brisbane, meaning the side will be as expected barring Warner's possible absence.
Team: David Warner, Cameron Bancroft, Usman Khawaja, Steve Smith (captain), Peter Handscomb, Shaun Marsh, Tim Paine, Mitchell Starc, Josh Hazlewood, Pat Cummins, Nathan Lyon.
(Editing by Peter Rutherford/John O'Brien)
