The two-time champion mutually terminated the contract of left-back Fabio who could be replaced by Adelaide United's Cassio at the start of next season.
Still smarting from their failure to reach the A-League finals, the Sky Blues have started the process of reconstructing the team.
Fabio, who signed a two-year contract with Sydney in 2012, was told by the club that it could not guarantee him a first-team spot next season and the player has agreed to have his contract terminated.
"Fabio wishes to thank Sydney FC for giving him the opportunity but since he would like to play regularly he took up the option of leaving the club a year before his contract expires," the player's agent Milton Da Rocha said.
"Fabio loves Australia and he has started the process of acquiring citizenship.
"He has asked me to find him another club."
Adelaide fullback Cassio, who became an Australian citizen last September, said he would not discount the possibility of joining the Sky Blues.
"I am under contract with Adelaide so I can't really talk much about this but I know (chief executive) Tony Pignata very well and I have a very good relationship because I always liked his work ever since he was with Wellington Phoenix," Cassio said.
"It would be good for both of us if we were to work together.
"Sydney showed interest in me two years ago but there is nothing at the moment however in football you can never tell what's around the corner.
"I have told Adelaide that my priority is to stay and take up the next two years of my contract but I also asked them to let me know as soon as possible what their plans are for me so I can talk to other clubs.
"The way things are going in Adelaide is not really good."
Sydney later issued a statement thanking Fabio for his services.
'I’d like to thank Fabio for his service to Sydney FC during the last 12 months," coach Frank Farina said.
'We are looking to change things going forward and we couldn’t guarantee Fabio the regular first-team football he requires.
'On behalf of the club, I’d like to wish him all the best for the future."