Australia star batsman Steve Smith has yet to feature after missing the first two games after being hit on the head during practice last Thursday.
Team management have repeatedly stated Smith has been rested purely as a precaution despite passing two concussion tests.
Langer said Smith was "tracking in the right direction" ahead of the decider.
"Fingers crossed. We know what a great player he is," said the coach.
Australia have now squandered winning positions in all three formats against England in just over a year, starting with a stunning one-wicket loss in the third Ashes Test at Headingley.
They threw away the opening Twenty20 match of the current tour and collapsed against 50-over world champions England in the second ODI on Sunday.
But Langer was adamant that Australia had no qualms when it came to close finishes against arch-rivals England.
"I don't think there's a mental fragility," he said. "These things happen. The hardest thing in cricket is hitting the winning runs. We were chasing under lights on a worn wicket. It was challenging and we weren't up to the challenge.
"We've got a very good team and are showing in most of the cricket we are playing that we are up to the fight. I don't think they (the defeats) are linked at all."