Ferreira joined the Mariners on a two-and-a-half year deal after securing a release from the Reds, who have called on Football Federation Australia to make a decision on whether A-League clubs will be permitted to sign four or five visa players in future.
FFA is keen to reduce the number of visa players from five to four per club in an effort to increase opportunities for young Australian players.
Adelaide coach Josep Gombau said he would have liked to have offered Ferreira an extension and provided the off-contract Portuguese star with the certainty he was seeking.
"It's something that I am asking Michael (Petrillo, Adelaide United CEO) every week," Gombau said, at the press conference to confirm Ferreira's departure.
"If we had five, we would have extended his contract for sure.
"I can't make a decision if I don't know this."
FFA's plan has been met by stern resistance from A-League club owners, who believe it would lead to a drop in the competition's overall standard.
"To be four months out from the end of the season and not know how many foreign players we can sign is not right," Petrillo said.
"I made the point to be honest last week to the FFA and I used Fabio as the example.
"Without knowing if it's four or five, basically, we've lost a player because of that.
"We can understand Fabio's concern about that because he's got a future to look after.
"We may not be the only club that's going through that sort of thing."
The Reds wasted little time in finding a replacement for Ferreira, announcing on Tuesday the recruitment of Spaniard Miguel Palanca for the rest of the season.
With four foreign players already on the books at Adelaide, it is anticipated Palanca's long-term future will be determined by whether the club will be allowed to sign a fifth.
Palanca, who will arrive in Adelaide later this week, made three first-team appearances for Spanish giant Real Madrid during the 2008-2009 season and played regularly for its second team in the Segunda Division.
The 27-year-old joins the Reds from Numancia, where he played 22 times over 18 months and scored five goals for the Segunda Division club.
"We are trying to play this particular style and to bring a player like Palanca will only help us improve as a team," said Gombau, a former Barcelona youth coach.
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