The German was hauled off at half time of Spurs' 1-1 Europa League draw at Rangers on Thursday, with Postecoglou later claiming the forward 'wasn't playing anywhere near the level he should'.
It was the first time the Tottenham boss had publicly singled out a player for criticism - however his brutal assessment serves as a warning for Werner and his teammates who are in the midst of poor form.
Postecoglou said of Werner in his post-match press conference: "His performance in the first half wasn't acceptable."
"We need everybody including him to be contributing, because we don't have the depth to leave people out if they're performing poorly.
"We need them to play their part. Especially the senior guys. When I'm asking younger guys to do massive jobs.
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"I expect a level of performance from some of the senior guys and today wasn't that."
Former Tottenham striker Teddy Sheringham joined talkSPORT on Friday and revealed he hoped Werner's early exit at Ibrox serves as motivation to improve his performances.
"In the main, every player is trying to implement what he [Postecoglou] wants out on the pitch," Sheringham told talkSPORT.
"I don't see anyone shirking apart from Timo Werner. He's been poor whenever I've seen him this year.
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"He needs to pull his finger out and realise what it is to be a professional footballer again and show some real umph because he looks like he's going through the motions.
"I don't agree with Ange's coming out and saying it publicly but having said that, he needs to know what other people are thinking."
Another former Spurs ace Alan Brazil provided his own stinging criticism of Werner saying: "With the greatest respect to Werner, I know he works hard but he's not a top player.
"He couldn't cross a road."
However, Postecoglou's public condemnation of Werner has not gained universal approval.
Troy Deeney, who became embroiled in a public spat with his players when in charge of Forest Green Rovers, believes Postecoglou's rant was a message to the board ahead of the January transfer window.
"I felt as a manager, that was a little bit of a dig at him," Deeney told talkSPORT's White and Jordan.
"A cheap one to send a message upstairs to say, 'this is what you've left me to work with and this who you you say I need to get over the line with.'"
Meanwhile, talkSPORT's chief football correspondent Alex Crook added: "He's going to need Timo Werner. Tottenham have got a crippling injury list. He risks losing him now with those comment's doesn't he?"
Tottenham are without a win in five games since winning 4-0 at Manchester City on November 23, meaning the pressure is piling on the Australian head coach.
Postecoglou is rueing an injury crisis that he described this week as 'the worst in my career' as he contends with a makeshift defence and key absences in midfield and attack.
Asked about Postecoglou's tenure so far, Sheringham heaped praise on the 59-year-old and called on the club to stick by their man.
"I'm here to back Ange this morning," he added. "I love what he's given Tottenham this year. I think over the last four or five years you've seen Tottenham under [Jose] Mourinho and [Antonio] Conte make one maybe two chances a game.
"I go to watch Tottenham now and I see them making ten chances in the first 15 minutes.
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"I think it's exciting. I think any team would struggle without their two main centre halves and their main goalkeeper.
"I'm still excited and optimistic for Ange and the way he plays the game and I think they should stick with him."