Neill secured a short-term contract with Championship outfit Watford a day before the Socceroos squad was announced on Wednesday, but it was not enough to convince Postecoglou he deserved to retain his place.
There must now be serious doubts over the veteran's participation in this year's World Cup in Brazil, with Postecoglou making it clear he will only pick players who are in regular action for their clubs.
While Neill's omission was not unexpected, there were a number of surprise selections.
Curtis Good (Dundee United), Chris Herd (Aston Villa), Massimo Luongo (Swindon Town) and Ben Halloran (Fortuna Dusseldorf) will all have the opportunity to make their Socceroos debut.
"The squad to face Ecuador represents the first steps in what I believe is the building of the next golden generation for Australian football acknowledging there is a need to balance experimentation and experience to achieve this," Postecoglou said.
"The Ecuador match gives this group of players an opportunity to stake a claim for the World Cup. They have been rewarded for playing consistent and strong football and shows that age and limited international experience are not barriers to opportunity.
"I was encouraged by what I saw on my scouting trip and what I've been watching in the A-League and other parts of the world and I’m confident that with courage and belief we can face the challenges ahead and not waver from our long term plan."
This friendly is the last match before Postecoglou selects his World Cup squad, although the coach made it clear that the door is still open for players not selected.
"Selection in the final squad for the World Cup is still very much an open door," Postecoglou said.
"There were quite a few players, particularly those in Asia whose leagues are just beginning, who are still very much on the radar.
"There are also a few players who are very much a part of my thinking and plans for the World Cup who are not playing and I was pretty mindful of not calling anyone who was not going to play some significant game time.
"Their club form going forward will be a big indicator of that and players still have an opportunity to get back into the squad."
Socceroos squad:
Oliver Bozanic (FC Luzern), Tim Cahill (New York Red Bulls), Jason Davidson (SC Heracles Almelo), Ivan Franjic (Brisbane Roar FC), Curtis Good (Dundee United FC), Ben Halloran (Fortuna Dusseldorf), Chris Herd (Aston Villa FC), James Holland (FK Austria Vienna), Mile Jedinak (Crystal Palace FC), Brad Jones (Liverpool FC), Mitchell Langerak (B.V. Borussia 09 Dortmund), Mathew Leckie (FSV Frankfurt 1899), Massimo Luongo (Swindon Town FC), Ryan McGowan (Shandong Luneng Taishan FC), Matthew McKay (Brisbane Roar FC), Mark Milligan (Melbourne Victory FC), Tommy Oar (FC Utrecht), Tommy Rogic (Melbourne Victory FC), Mat Ryan (Club Brugge KV), Adam Sarota (FC Utrecht), Matthew Spiranovic (Western Sydney Wanderers FC), Dario Vidosic (FC Sion), Luke Wilkshire (FK Dinamo Moscow)
