Mitch Marsh failed again on Sunday as Australia's hopes of a fourth Test win against India took a massive hit.
Marsh, nicknamed Bison, was caught behind off Indian ace Jasprit Bumrah for a fourth-ball duck.
Other than his second-innings 47 in the first Test, Marsh has not scored more than nine in the series.
The medium pacer also has taken just three wickets and only bowled seven overs in India's first innings.
After his dismissal for four in the first innings, Marsh badly needed a decent knock on Sunday to keep the hounds at bay.
Whatever the result on Monday, he is the most vulnerable member of the Australian XI heading into next week's fifth and final Test at the SCG.
But Langer wants the selectors to retain Marsh for Sydney.
Marsh has appeared an anguished figure for most of his time at the crease in this series. (Dean Lewins/AAP PHOTOS)
"It's a closely knit team. I've been public in saying, even though India are starting to fight back in this, I don't like the chopping and changing of Test teams," Langer said on the Seven Network.
"In that instance, it will be another change to the Test team. I don't think it will be a positive one. I think he should play in Sydney."
Marsh scored a century in Leeds during last year's Ashes series on the way to winning the Allan Border Medal.
Langer wants his fellow West Australian to regain the attitude that has brought him success, noting Marsh's memorable acceptance speech at the Border Medal count.
"He said when he won last year's AB Medal, his words were, 'I'm a bit fat and I like a beer'. That's how I want to see him play cricket - with a smile on his face," Langer said.
"If I was the head coach or the selectors, I'd be saying 'Mitch, it's a big game for us. Get in with your mates. Play with that carefree attitude and show us what you've got'."
Webster was drafted into the squad as injury cover for Marsh ahead of the second Test and was also in the mix for Melbourne.
Marsh had a sore back after the series opener and has been playing mainly as a batter since.
Webster, 31, has been a standout in the Sheffield Shield for the past 18 months.
Last summer, the Tasmanian became only the second player after West Indian great Sir Garry Sobers to score 900 runs and take 30 wickets in a Shield season.
He is yet to make his Australian debut in any format.
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