Sandler moved to City last year from PEC Zwolle and worked closely with Kompany when they were together at City.
He said upon the Belgian's departure: “I couldn't have wished for a better mentor than you when I joined Man City. A leader among men and an inspiration.
"You taught me so much. Disappointed that you are leaving, but proud of what you have achieved here and eagerly awaiting your new adventure.
"Good luck Vincent."