The Victory confirmed Mata's playing career at the club would be a one-and-done affair in a statement on Friday afternoon, meaning the league is now without its biggest and most recognisable name.
Mata comfortably claimed the Johnny Warren Medal as the league's best player in a magical first season at Victory in 2025-26, notching 13 assists and five goals, after a previous indifferent stint at Western Sydney.
The Spaniard, 38, had wanted to take time to contemplate his future, which new coach Giovanni Savarese had respected, though those around the Victory had been growing increasingly pessimistic Mata would return.
Mata, who joined the club's ownership group in June, will maintain that interest in the Victory along with taking up the role of chair of a recently-announced football committee.
"I loved every minute and so greatly enjoyed everything that we achieved last season, falling back in love with football at such a special place, in an amazing city that it was a privilege to call home," Mata said in a statement.
"Thanks to my teammates, the staff and the board for welcoming me so warmly, supporting me so generously, and allowing me to give my best for this wonderful club and the amazing members and fans whose support I still feel every day.
"Now I am excited about our next chapters, believing together in the future of Australian football and inspiring the next generation of Melbourne Victory players and supporters."
Without Mata, the Victory have already qualified for the Australia Cup final against either South Melbourne or Lions FC, after beating Sydney FC 2-0 in Wednesday night's semi-final.
The club had been looking at contingency plans, including former Auckland playmaker Guillermo May, to fill the final remaining visa spot - and the massive creative hole - left by Mata.
With the new season - starting with an October 18 trip to Wellington - rapidly approaching and the Victory juggling the league with an Asian Champions League Two campaign, that is now a matter of urgency.
Former Chelsea, Manchester United and Spain star Mata, whose decorated CV includes winning the World Cup and Champions League will remain in Europe while he considers his next playing move.
"Juan's 2025/26 season will live long in the memory of Victory fans and should be cherished by all supporters of the world's game here in Australia," football director John Didulica said in a statement.
"The way he performed on the pitch and the way he conducted himself around the club were both exemplary.
"We thank him for everything he delivered and we're delighted that, after he chose to join Melbourne Victory, he was able to excel within the strong culture and high-performance environment established here over several years.
"Everyone at the club is excited that he is part of our ownership group and, in the future, looks forward to his football intelligence leading our football committee."
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