Middleby was making his way back to his car when two fans - wearing Sydney scarves over their faces - leapt out and surprised him.

Before hitting Middleby - due to join North Queensland Fury next season - one said: "'You're f***ing leaving us, are you Middleby?"

The attacker then launched a flurry of punches, knees and kicks at the Sydney FC midfielder before the pair ran off when Middleby's wife intervened.

"His mate just stood there, and he kneed me and starting throwing punches," Middleby told the Sydney Morning Herald.

"I thought he was going to attack her, so I threw a punch or two, and then my mate, who was also at the car, came over as well.

"That's when the two of them ran off."

He added: "Never in my career have I experienced anything like this. It's a disgrace."

Sydney FC today confirmed the attack and launched a probe to find the culprits. They hope security camera footage at the ground may be able to pick up the attackers.

"Middleby was unhurt, but was left shaken by the incident and Sydney FC have been taking all possible steps to identify the men involved since the incident on Sunday night," said a statement from the club.

"The cowardly confrontation is completely unacceptable and the club will continue to working closely with SFS management and the FFA to ensure that those responsible are held accountable.

"The club will ensure that every avenue of investigation is pursued to identify the culprits, and the strongest possible penalty will be applied once they are found, with the pair facing life bans from all Sydney FC matches and possible legal action."

The statement added: "Sydney FC enjoy a great relationship with their supporters, and will continue to do so into the future despite the behaviour of two individuals who have forfeited the right to call themselves Sydney FC fans.

"Sydney thank their fans for their ongoing support and are urging anyone with any information about the incident to contact the club and assist with the investigation."