He is upset at how Mata has been treated at the Australian club, where he arrived in September.
The 36-year-old, a Champions League, World Cup and a European Championship winner, has barely played for his new team.
“I think it's just insane… I don't understand,” his agent Fahid Ben Khalfallah fumed while speaking on the A-League Off Air podcast.
“When you bring (in) someone like him, you have to play him in a system that suits him. I couldn't believe he only came on for eight minutes or whatever.”
“I think it's disrespectful. I hate it. I really, really hate it because it makes no sense to me.
'And I'm so sick, so sick of those coaches saying, 'Oh yeah, but the intensity (of the A-League)'... OK, we will talk about someone who won the World Cup, won the Euro, Champions League, played in England for 10 years – he's always been one of the most intelligent and most technical players of his generation.
“He wasn't quick, he wasn't the strongest. So despite that, he was one of the best players in the world.
“And we're talking about A-League intensity? You must be kidding.
“Put horses on the pitch, they will be running – but they can't kick a ball, and they can't play. They can't pass the ball.
“Seriously, I'm disgusted to hear that kind of stuff.”