The Italian international made his move to Germany this summer, having previously spent time at clubs including Torino, Juventus and boyhood favourites Pescara.
"I will always remain a fan of Pescara," Immobile told the Bundesliga's official website.
"My time there was crucial to my development and improvements as a player. It was the platform for a career at the highest level. I will forever be grateful to [then-Pescara head coach Zdenek] Zeman."
Last season the striker became the Capocannoniere after notching 22 goals in Serie A.