Sydney FC are working with police and Football Federation Australia (FFA), leaving no stone unturned to find the men who "cowardly" attacked Robbie Middleby.
The midfielder was confronted by two supporters after Sydney's 1-0 A-League win over Wellington Phoenix in the carpark of the Sydney Football Stadium (SFS) last Sunday.
Middleby, who did not play against the Phoenix, will leave Sydney at the end of the season to link up with North Queensland Fury.
The 34-year-old said on Thursday that one of his attackers jumped out from behind a car and shouted abuse about his decision to leave the club after a four-year spell.
"His mate just stood there, and he kneed me and started throwing punches," Middleby told the Sydney Morning Herald.
"I tried to back off but then my wife, who was waiting at the car but saw what happened came running over .. and I thought he was going to attack her so I threw a punch or two."
Police have since advised the 34-year-old not to discuss the incident as investigations are still ongoing, but Sydney chief executive Stefan Kamasz told a media conference on Friday the club was doing all it could to find the attackers.
"Since Sunday we have been in discussion with the FFA, the FFA's security consultants, the SFS security, the police as well as making our own enquiries," he said.
"This confrontation .. was a cowardly act by two individuals and they cannot possibly be called fans of Sydney FC .. there is no place for such cowardly behaviour in football.
"If we can ... we will use the full force of banning orders that are possible and like to see that the guys are prosecuted.
"We have a fantastic relationship with our fans and especially the Cove ... and I have received a number of calls from Cove members demonstrating their support for Robbie.
"Robbie has been a great servant to this club and a great ambassador, anyone who knows Robbie will understand that he gives 100 per cent whenever he goes out for this club.
"Everyone is sad that Robbie is leaving for the Fury next season but we respect his decision and Robbie has an important role at the club for the rest of this season."
North Queensland Fury boss Don Matheson expressed his shock over the attack.
But he hinted that it may have been prompted by Sydney FC's disappointing form rather than Middleby's decision to leave the club.
"I would be disappointed if those fans used Robbie as a scapegoat for the club's position in the moment," he told AAP.
"We are terribly disappointed especially considering Robbie is a sensational bloke who has given his heart and soul to Sydney FC.
"It's a shame that something like that has happened to finish off his career there.
"But at the end of the day we look forward to him coming here."
Matheson described the attackers as "thugs".
"I couldn't describe the type of supporter who would stoop to that level and behave like that, they are obviously thugs," he said.
"It is difficult to understand that they have to behave like that to get their point across.
"It's not something we would tolerate or condone in our region."