Coach Ange Postecoglou revealed on Tuesday he's told Neill he won't be selected to play at a third World Cup, saying the decision "weighs heavily" on him.

But he wasn't convinced the 36-year-old defender could cope with the rigours of soccer's showpiece event in Brazil next month.

Midfielder Mile Jedinak is favoured to be named captain, though Postecoglou says he's in no rush to appoint his World Cup skipper.

Informing Neill of his non-selection was tough.

"He was obviously very disappointed," said Postecoglou.

"It was difficult. He has worked damn hard to try and get himself ready and available. He has shown an enormous determination to go to this World Cup.

"I just had to make a decision not so much about the recent history, but the last six months.

"In terms of form and fitness, there just wasn't enough evidence there for me to say that he would be able to hold up in the World Cup."

Neill, captain of Australia's qualifying campaign, has led Australia 60 times - equal-most with 1970s leader Peter Wilson.

Postecoglou will name his 30-man preliminary World Cup squad next week but took the decision to tell Neill his fate early out of respect.

"I'm not going to do that with everyone but he is a unique case," said Postecoglou, adding that Neill intended to continue his career in Europe.

Neill, capped 96 times for Australia, struggled to find a club and enough game time since a stint in Japan ended last November, finally signing with English championship team Watford in February before a loan move to Doncaster Rovers.

"He was probably a little bit unlucky in a couple of the moves he made," Postecoglou said.

"And certainly from my perspective, if post-Christmas, from January onwards, if he'd had four months of football under his belt, I guess a different decision would have been made.

"It's not easy.

"He has shown outstanding determination and it's a credit to him.

"You can see why he has played for his country as many times as he has and why he was a leader. He has certainly gone down fighting."

AAP