STEVEN Lustica's shock exit from Adelaide United is being investigated by officials from soccer's players' union after he walked out on the club.

Adelaide United officials on Wednesday stated Lustica wanted an immediate contract termination to join Brisbane Roar.

But it's understood Lustica has not signed for Roar. He has not trained with Adelaide this week.

Table-topping Brisbane boss Mike Mulvey did not want to comment after the club on Wednesday announced it had signed Costa Rican striker Jean Carlos Solorzano.

But Lustica, along with six of his Reds teammates, are now able to start negotiating for new deals with less than six months remaining on their Adelaide contract.

A spokesperson from Professional Footballers Australia - the Australian soccer players' union - confirmed the organisation was dealing with Lustica's predicament.

But the PFA spokesperson declared it was not ready to make a comment on the delicate situation.

Lustica and his Australian-based agents did not return calls to The Advertiser after Adelaide United's football director Michael Petrillo issued the pointed statement which aired intricate details.

In the statement Petrillo said the 22-year-old had been offered a new Reds contract extension and had indicated he was ready to sign.

But according to Petrillo, Lustica had changed his mind after Roar made an offer.

Lustica has played 15 games for the Reds since joining from Croatian club Hajduk Split last year.

He was on the bench in the 2-2 draw with Melbourne Heart on Saturday at Coopers Stadium but came on in the second half.

Lustica was also benched in Adelaide's 1-0 win over Western Sydney Wanderers at home on January 19 after reportedly attending his sister's wedding in the ACT.

But the former Gold Coast, Brisbane Roar and Hajduk Split (Croatia) midfielder has had an outstanding season with the Reds since signing for Adelaide in September.

Lustica has formed a formidable partnership with elegant playmaker Marcelo Carrusca as attacking midfielders.

Carrusca is also set to be on his way at the end of the season after the Argentine rejected Adelaide's contract extension when his salary did not matched his first contract in 2012 when CPI was taken into account.

After Carrusca's agent Maxi Pra declared the Argentine's first priority was to remain with Adelaide the Buones Aires-based manager said Carrusca would wait for another Reds offer this week before making a decision.

Carrusca is in high demand and is also fielding contract offers from abroad and Sydney FC.

And Adelaide still has not announced whether is has re-signed more players coming off contract at the end of the season.

Nigel Boogaard, Jon McKain, Daniel Bowles, Jake Barker-Daish and Ryan Griffiths' contracts are up for renewal.

Michael Zullo's one season loan deal from FC Utrecht also comes to an end.

News_Story: Gird your loins