This was announced by Borussia on Monday. The Gladbachers did not provide any information on the transfer modalities.
Hack, who trained at TSG Hoffenheim and also played for 1. FC Nürnberg, has played for Arminia Bielefeld for the past two years. In the past second division season, Hack scored ten goals for Arminia, but could not prevent relegation to the third division.
“Robin Hack is a dynamic and dangerous attacking player who already has a lot of first and second division experience,” said Borussia’s sporting director Roland Virkus. “His personal development over the past few years has been good and we still see a lot of potential in him.”