The 19-year old midfielder was set for a move to Italian outfit Parma but sustained a quadriceps injury prior to the U20 World Cup in Turkey in June and that transfer has now stalled.
The issue is being dealt with by the Professional Footballers Association (PFA) and for the time being, the Sky Blues will guarantee Antonis a spot on their list in case the move completely collapses.
"I'm keeping a spot for Terry - I've told him that," Pignata told au.fourfourtwo.com. "So it's just a matter of getting the verdict from Parma and then we can go forward.
"Technically he's still a Sydney FC player. We haven't issued an international transfer clearance. I'm not exactly a hundred per cent sure in terms of the process and what's been signed over there and that's what we're trying to find out at the moment.
"I would have liked (a decision) by the end of this month but I don't think a solution is too far away to be honest. If you were a betting man, which I'm not, I think you'd be saying he's playing for Sydney this year.
"Put it this way - they've started preseason and he's not there."