Stoinis missed Wednesday's victory over Pakistan due to a side strain he suffered against India three days earlier, prompting the reigning champions to fly in Mitchell Marsh as cover.
Stoinis did some batting in Taunton's indoor nets on Wednesday, but the seam bowling all-rounder will miss a second match, captain Aaron Finch said on Friday.
"He hasn't bowled yet in his recovery over the last couple of days. Just waiting for the injury to settle down a bit more," Finch told reporters during training.
Australia have a five-day break before their next game against Bangladesh.
"We've talked a bit about it, but we'll just see how he pulls up over the next few days," Langer said of Stoinis.
"We know that it's important to have an all-rounder in the side if we can, and if we can't we've got to adapt."
In the absence of Stoinis, who is also an excellent outfielder, Finch and Maxwell combined as the team's fifth bowler against Pakistan, conceding 71 runs between them from nine overs, with Finch taking one wicket.
"We've got a very, very strong batting side with the batting line-up we had I thought," Langer said.
"It's probably harder for Finchy than anyone else to have less recognised bowlers I'll say. Everyone's got to be on top of their game."
With wicketkeeper Alex Carey and quick Nathan Coulter-Nile proving their skills with the bat, playing five specialist bowlers is one option for the holders. But Langer was not totally convinced.
"We'll have to work it out, but it certainly makes it more problematic not having an all-rounder in there," Langer said.
"You could (play five specialist bowlers), but it's very rare for an Australian team to do it," he said.
"We did it a few times last year when we were in England. You certainly can in T20 cricket. It's tougher in 50-over cricket, but you never say never. We'll try and work out the best combination to beat Sri Lanka."
(Reporting by Amlan Chakraborty in Manchester; Editing by Hugh Lawson and Pritha Sarkar)
