The Ludwigshafen-born forward joined BVB from VfL Wolfsburg in 2016 and scored eight goals in 51 appearances during his time at Signal Iduna Park, although he spent the past two campaigns on loan at Fulham and then Spartak Moscow, respectively.
Spartak reportedly had an option to extend the former Mainz and Bayer Leverkusen forward's loan deal for another season, but opted against it due to a serious injury that had ruled him out since last year, meaning he is now a free agent heading into next season.
The 29-year-old is the second member of Germany's 2014 World Cup-winning side to be released by Dortmund this season after Mario Gotze, who scored the winning goal in the final of that showpiece against Argentina from Schurrle's cross, was also allowed to depart.