Janko, Sydney to part ways
The Austria captain netted 16 goals during the season to win the golden boot in his maiden A-League campaign.
But his nation are still involved in qualifying for Euro 2016, meaning he would have missed several games again in 2015-16.
The club announced the move in a statement on Sunday.
“Marc has done very well this season and we were happy with his performances and his contribution to Sydney FC," Sky Blues coach Graham Arnold said.
“However he will miss a number of A-League games next season due to international duty with no FIFA breaks in the A-League. Add that to our busier schedule, including Asian Champions League commitments and after lengthy consideration we have come to this decision.
“On behalf of the club and the team I’d like to thank Marc for his service and the professional way in which he has conducted his business. We wish him and Austria all the best for the future."
In a statement on Twitter, Janko expressed his disappointment with the handling of his contract – saying he was prepared to re-sign.
The 31-year-old said the club then withdrew the offer.
"Dear fans, unfortunately I have to announce that I won't return to Sydney anymore," he wrote.
"A few weeks ago the club made me an offer that I was willing to accept. It was the same one like one year ago by the way. As I informed the club that I would be happy to stay another year I was told that all signings will be handled after the last game of the season.
"Very surprisingly the club called today to inform me that they are pulling back their offer because they are too concerned about my international duties for the upcoming season.
"It's very disappointing for me and my family how these things have been communicated and handled in terms of honesty and respect but I guess that's the football business.
"After a quite successful year, in which I made history with the club I will move forward now.
"I wanna wish all the fans and players good luck for their future and all the best. It was a pleasure being part of Australia's biggest club."