Haddin enjoyed outstanding Test series against England and South Africa earlier this year, but he has failed to continue that fine form in Bangladesh.
He missed a regulation stumping chance to dismiss Chris Gayle on 26 in Friday's narrow defeat to the West Indies.
"His keeping has been poor. That's okay, he won't mind me saying that," Lehmann told reporters. "He's honest enough for that. He's been fantastic over a long period of time for us.
"He took a great catch [to dismiss Marlon Samuels] and missed a couple of opportunities.
"At the end of the day he's been exceptional for us. He'd be disappointed in his own form in these two games. That's not hiding away from the truth."
Australia play tournament favourites India later today, before completing their Super 10 campaign with a match against hosts Bangladesh on Tuesday.