Seemingly lost to Australia after switching allegiances to land of his birth, and even making his debut for Greece in a friendly international against Turkey last November, the dual nationality forward is now set to play for the Socceroos in this month’s FIFA World Cup qualifiers against Tajikistan and Jordan.
The media coverage of his switch painted a picture of Socceroos coach Ange Postecoglou simply jetting to Greece, where Giannou played for Asteras Tripolis before his February move to Guangzhou R&F, and using the gentle art of persuasion to tempt the former Australia and Greece youth international back to the nation where he spent his formative years.
The reality of reuniting Giannou with his former Joeys coach is far more convoluted, complex and involves countess hours of digging, delving and diligence. Not to mention paperwork, emails and negotiations pinging back and forth between Australia, Greece and Zurich over six months.
Now, after 14 goals in 22 games for Asteras, Giannou, 26, is being touted as a possible successor to ageing icon Tim Cahill - after he was granted permission by FIFA in January to complete his switch from Greece back to Australia.
Time will tell whether he becomes Postecoglou's go-to man for goals, but the fact he is even a chance is down to the persistence and tenacity of a Melbourne-based player agent who dug deeper than Poirot on a cold case, the legal eagles at FFA, with a little helping hand from SBS.
With Giannou mindful not to trumpet his intentions, the work by his representatives at FIA Sports Management and FIFA-registered intermediary Jon-Paul Michail, in tandem with the FFA, was kept under tight wraps.
It would all have been academic had Giannou been given any minutes off the bench by Greece a year ago in a UEFA EURO 2016 qualifier against Hungary.
But the door remained open and the clandestine journey to bring him back into the green and gold fold painstakingly unfolded from mid-2015.
It picked up steam In October 2015 when The World Game published an article on his form for Asteras, highlighting the ambiguity over his international allegiances. Giannou declared his ardour for both nations but behind the scenes, and off the record, he was leaning heavily towards Australia.
The article opened some minds and provoked calls in Greece for him to be handed a debut without further ado, while in Australia Michail made contact with the FFA to alert them to Giannou’s ever-growing reputation in Greece, not just in the league but also in national team circles.
"There was a lot of confusion about Giannou’s eligibility initially, with even suggestions that Giannou had chosen not to represent Australia and unequivocally pledged his allegiance to Greece – which never occurred," Michail said.
"This misleading information was also communicated to Ange Postecoglou who had enquired about Giannou’s eligibility when first appointed to the job in 2013. Because of this no further action was taken at the time."
Once that was cleared up the investigation in to his eligibility began in earnest.
According to FIFA edicts, a player may switch national allegiances only once. Having first represented Australia and then Greece at youth level, a key factor was to discover if the Greek FA had pursued the proper paperwork to switch Giannou’s allegiance from Australia to Greece.
Giannou had no recollection of any such paperwork being discussed or executed.
Upon further research by FIA Sports Management, when Giannou first played for a Greek youth team in 2008, FIFA regulations did not require paperwork or official change of association declarations to be completed.
This turned out to be a mystery-busting discovery which was followed two months later by Postecoglou reaching out to FIA to confirm his interest in Giannou as a Socceroos prospect.
Ironically, just two days later, Giannou was called up by Greece for friendly matches against Luxembourg and Turkey.
FIFA law dictates that a player must heed national team calls and attend any and all camps. So that's what he did.
He made his debut for as a 70th minute substitute against Turkey in Istanbul on 17 November. But, since it was purely a friendly, it did not derail the campaign.
Over the next two months, the FIA and the FFA compiled what they thought was a compelling case to put to FIFA. It included proof of citizenship, migration paperwork, movement records and Australian and Greek youth team personal records.
The verdict they were hoping arrived in the affirmative in late-January. It was at that point that Postecoglou booked his passage to Athens to meet the forward he had last worked with nine years earlier to discuss the future, with both on the same page.
But subterfuge surrounding his international future remained right up until the eleventh hour with fears in the Giannou camp that a leaking of his switch before his move to Guangzhou R&F was ratified might have provoked a miffed Greek FA into stalling over his International Transfer Certificate (ITC) and even scuppering the deal.
By then, though, Postecoglou had got his man.