Surplus to requirements at the Europa League winning club, Hrustic - who has a year remaining on his Bundesliga contract - has been given permission to talk to other teams by manager Oliver Glasner.
He has since been exploring his options and looks to have played his last match for the German side joined from Groningen nearly two years ago.
Reports out of Spain suggest Real Betis - which finished fifth in La Liga last season - is in the mix, having initially showed interest in the 26 year-old in December.
Serie A minnow Salernitana - which escaped both bankruptcy and relegation at the eleventh hour last season - is also willing to offer a new home to the elegant attacking midfielder.
Hrustic is urgently looking to maximise his match minutes heading into November-December’s World Cup in Qatar, in the knowledge that game time with Die Adler will be minimal at best this season.
The 19-cap Socceroos star was omitted from Glasner’s first two squads of the new season for the 4-0 Cup romp over Magdeburg and 6-1 opening round trouncing at the hands of champion Bayern Munich.
With the future of longtime national team playmaker Tom Rogic in the ether after his departure from Celtic and decision to sidestep Australia’s World Cup playoff wins over UAE and Peru, the importance of Hrustic has never been greater.
Acknowledging that new reality, Socceroos assistant Rene Meulensteen told beIN SPORTS: “It’s vital for Ajdin to be somewhere were he commands regular playing time, and starts to enjoy his football again because he’s a really important player for us.
“You want people like him to be playing - there’s still so much to come from him because he’s a player who possesses real quality.
“The more he plays before the World Cup the better it is because when he’s in his match rhythm he can really hurt the opposition with his creativity and ability conjure something unexpected.”
Hrustic scored three goals during Australia’s torturous journey to qualify for Qatar, adding four assists, and has made 34 Bundesliga appearances for the Germans - though, tellingly, 24 of those came off the bench.
While back in the UK after a brief trip to Australia, there are no indications of where next for Rogic, 29, with his British agent Josh Barnett declining to comment on the path ahead.
There have even been suggestions the mercurial Rogic might simply slip quietly into retirement after his nine-year stay with the Hoops.
Meulensteen remains in 'the dark' over when, or even whether, he will resurface for club or country again.
“We don’t really know why he pulled out at the last moment (for the playoffs against UAE and Peru for apparent ‘personal reasons’),” he said. “And we don’t know where his thoughts are with the future. We’re in the dark.
“We’ve offered all the help we can through Football Australia and the PFA and we really aren’t any the wiser.”