His dramatic announcement comes just two years after the football club's German international goalkeeper Robert Enke committed suicide aged just 32 after suffering from depression for years.
Miller, 29 and who moved to Hannover from Karslruhe in the summer of 2010, said that he had informed the club of his illness and his plans to remedy it for which he had received their full support.
"I decided to inform the club, our fans and the media with regards to my illness," he told the club website. "I am going to hospital immediately to undergo treatment."
Hannover wished him a full recovery.
"We give him our full support," said sporting director Jorg Schmadtke. "He has spoken frankly of mental problems which in our society are considered taboo topics. Our priority is that he is fully cured."
Hannover coach Mirko Slomka said he was impressed by Miller's courage, who had come to tell him personally, as was German national coach Joachim Löw.
"It was the best thing to do (going public), even if opening oneself up to the public is not easy," said Löw, speaking in Gdansk ahead of Tuesday's friendly with Poland.