The FFA issued a show-cause notice on Wanderers, foreshadowing a likely hefty fine.
The FFA issued a show-cause notice on Wanderers, foreshadowing a likely hefty fine, ahead of the Sydney club's Asian Champions League opener against Urawa Red Diamonds on Tuesday.
Fans raised the obscene banner at the ANZ Stadium when the Wanderers ended Sydney FC's 19-game unbeaten streak with a 1-0 victory in front of a near 45,000 crowd on Saturday.
Security staff managed to remove the banner depicting a blue-faced man resembling Sydney FC's Graham Arnold performing oral sex.
The Red and Black Bloc supporters group also posted a photo of the banner on social media alongside a quote from Arnold.
After an investigation, the FFA gave the Wanderers until Thursday to answer the show-cause notice declaring the banner "totally unacceptable and offensive to any reasonable member of the public".
The federation is also looking into other "anti-social behaviour" at Saturday's match which saw seats ripped up and 15 arrests.
A-League officials were expected to impose a large fine on Wanderers as well as restrictions on Red and Black bloc fans.
Coach Tony Popovic tried to set aside the controversy as he prepared the Wanderers -- the 2014 Asian Champions League winners -- to tackle the Red Diamonds in Sydney.
"It's a really tough group, probably the toughest in the Asian Champions League this year," Popovic told reporters of Group F which also features Shanghai SIPG and FC Seoul.