The 30-year-old former FK Zeljeznicar and FK Radnik hitman joined the Rockets last term and helped the club to a fifth-placed finish.
But he was reported to have agreed with the club to terminate his contract with one year remaining.
Zajmovic posted news of his departure with a post on social media, saying: "Unfortunately, my chapter at TS Galaxy has come to an end.
“I would like to thank the chairman, the head coach, the club director, the whole staff and last but not least my AMAZING TEAMMATES. It truly felt like being part of a family.”