Hanke, 29, has just three months left on his contract and claimed the club withdrew an offer tabled earlier in the season.
While his departure might not come as a surprise to Gladbach fans – he has only scored 11 Bundesliga goals in two years and just two this season – Hanke claimed he was betrayed by the club.
“I am very disappointed. I wanted to extend my contract, and was made an offer which was surprisingly withdrawn,” he was quoted as saying by AFP.
“I was totally shocked. This is a day of mourning for me and I am deeply saddened by the way management has dealt with me.
“All they have said is simply that the coach does not want me any more.”
The coach in question, Lucien Favre, gave little away.
“Mike has done a lot for Gladbach, but the club has done a lot for him,” he said somewhat cryptically. “It is a purely sporting decision.”
The club’s sporting director Max Eberl was slightly franker about the move.
“I offered Hanke a deal in the autumn but, in the meantime, our playing philosophy has changed.”
The decision to let Hanke go probably owes more to the form of young players Amin Younes (19) and Peniel Mlapa (22), both of whom have provided able support to main striker Luuk de Jong.
Ex-Schalke and Wolfsburg forward Hanke has been linked with a return to former club Hannover, who could cash in on Mame Biram Diouf this summer.