Brendan Schwab, PFA’s former chief and special council, confirmed on Friday that he is due to meet with Sydney FC officials in a bid to solve the impasse over the mooted $300,000 switch.
Australia U20 star Antonis is said to be so upset over his move being jeopardised that he is seeking advice on the possibility of suing the club if it continues to stand in his way.
Antonis, who is with the Young Socceroos in Cyprus ahead of the FIFA U-20 World Cup in Turkey, thought he was about to fulfil a lifelong ambition when Parma’s initial offer triggered a release clause in his Sydney FC contract in March.
Sydney FC CEO Tony Pignata said: 'Parma want to pay us in installments and if it was millions of dollars we would understand, but it’s not and we are not prepared to accept their payment plan.
'We believe we are within our rights not to do so, but I am of course prepared to talk with the PFA if they want to discuss the matter.
'The transfer is done but we are not willing to ratify the International Transfer Clearance until we receive a lump sum."
Pignata said he knew nothing of PFA’s involvement and denied he has a meeting scheduled with Schwab.
Terry Antonis's father and manager, Peter Antonis, said: 'As far as we are concerned Parma’s offer has triggered the release clause in his contract and that should be the end of it.
'The PFA are going in now to sort this out and we will let them do their work. Terry’s over there in Europe representing his country and this is very frustrating for him."
It is understood PFA believes Antonis has a strong case, with Parma pledging to pay $100,000 up front in July, when Antonis is scheduled to join the club, with the next two payments scheduled for October and February - a payment practice common in football’s market place.
Antonis missed the Young Socceroos’ 3-1 loss to Netherlands U-21 on 17 May due to a stomach virus.
He is in consideration for the international against Germany’s under-21’s on 31 May.
Antonis is understood to be so distraught at the thought of the transfer breaking down, he is considering returning to Australia to fight his cause.
Parma initially approached Sydney seeking to ink a deal with Antonis two days after it crashed out of A-League finals contention to Brisbane Roar in March.
It has been claimed that Sydney, which had a preference for Antonis to trial instead with Eredivisie outfit FC Utrecht, took three weeks to acknowledge the offer.
At the same time, the club initially stated the Parma offer was a trial – not a fully-fledged offer.
Sydney wants Antonis – who has not been paid since 14 April - to remain in the A-League for another season after a strong finish to the 2012-2013 campaign.
'I have spoken to Terry’s father about the non payment and have explained the situation," Pignata said.