Football Federation Australia has roundly condemned the homophobic banner brandished by Wanderers fans and foreshadowed punishment for those involved.
The banner, depicting a blue-faced man giving oral sex, was put up in the Wanderers' support area at ANZ Stadium during the second half of the game, won 1-0 by the Wanderers.
It remained aloft in front of the 44,843-strong family-friendly crowd for a number of minutes while security appeared to watch on before it was eventually taken down.
The FFA on Sunday made clear their disgust at the "discriminatory" image depicted and leaving open the possibility for sanctions against the club or its fans.
"FFA is aware of the unauthorised and totally unacceptable banner that was displayed in the Western Sydney Wanderers area during Saturday night's Sydney derby at ANZ Stadium," A-League chief Greg O'Rourke said.
"The discriminatory nature of the tifo has no place in society and will not be tolerated in the A-League.
"We are working with the club and currently gathering as much information as possible and will deal with the matter when we have all available facts including CCTV footage."
The Wanderers' active supporter group, the Red and Black Bloc, publicly saluted the banner on Sunday, posting it to its Twitter account alongside a quote from Sydney coach Graham Arnold.
The club itself declined to comment after the game on Saturday night, but confirmed on Sunday it was working with FFA to investigate.
"Due to the inappropriate nature of the item it was swiftly removed by our supporter management team and disposed of," chief executive John Tsatsimas said in a statement.
"As a club made up of the most diverse and inclusive cross-section of members and fans in Australian sport, we do not condone the imagery depicted in the banner.
"The club remains committed to working with FFA and our stadiums to ensure our matches remain a positive, family-friendly environment."
The Wanderers are sweating on a suspended points deduction, in place until the end of this season as punishment for fan trouble associated with lighting flares.
