Sasa Ognenovski, Matt Spiranovic, Jade North, Mark Milligan, Robert Cornthwaite andf briefly Rhys Williiams have all had an opportunity to show what they can do in the centre of defence.
But Osieck has not yet made up his mind on the best combination.
With the crucial World Cup qualifier against Oman in Sydney in March fast approaching, Osieck picked a 19-member squad for the friendly match against Romania in Malaga, Spain, on 7 February (AEDT).
"That is absolutely correct," Osieck said when it was suggested to him during a teleconference that he still had not settled the central defence question.
"Looking back at our recent games after the qualifier against Iraq, Cornthwaite left a good impression in Hong Kong.
"Michael Thwaite has played fullback and as a holding midfielder in Hong Kong, but he can play centre-half as well.
"There are others whom I did not pick for several reasons, mainly because it does not make sense to ask them to travel half way around the world for one single match."
Osieck said he was likely to give Williams and Ryan McGowan a chance to impress alongside Neill.
"Williams was part of our team but he was very unfortunate to be injured for a significant time," Osieck said.
"He is now playing regularly (for Middlesbrough) and I would like to have another look at him in the centre-half position.
"I would also like to see young McGowan in there, too.
"Neill will be suspended for the Oman game but I think that as captain he is the right man to give us guidance in the Romania match.
"He should also provide the experience in what is relatively a young side."
Osieck did not pick defenders Spiranovic and Ognenovski for different reasons.
Spiranovic, who plays his club football for Al-Arabi in the United Arab Emirates, is nursing an ankle injury, while Ognenovski, who plays for Umm-Salal in Qatar, was overlooked so Osieck could have a closer look at other candidates.
"Spiranovic is definitely injured and Ognenovski is a regular in his club team," Osieck said.
"But I know what he can do so if I bring in Neill and Ognenovski I won't be able to test the others that I want to have a look at. That would be a useless exercise."
Osieck said he was pleased to recall attack-minded fullback Michael Zullo to fill the left-back role that has been a problem for the national team for many years.
Zullo, who plays in the Netherlands for FC Utrecht, is seen by many as the man best suited to occupy the position.
"I'm looking forward to seeing him play," Osieck said.
"He was out for a significant period but he is now back in his team.
"I know what he can do and I included him also for a psychological reason "¦ I want him to feel that he is still a part of the team."
David Carney, who played many games at left back with mixed returns, appears to be losing his battle to re-establish his international credentials.
He last played for Australia in the 2-1 World Cup qualifying defeat by Jordan in Amman on 11 September.
His whereabouts are unknown although he has been linked with the Persepolis club of Iran.
"This is a difficult one because I have no recent information about him," Osieck said.
"I think he is still trying to find a club and, yes, he definitely is running out of time to get back in the team.
"The transfer window is closing in the next two days and I don't know what other options he may have.
"He has lost at least seven months of football, which is really unfortunate and never very productive."