Haller scored twice in Dortmund's 3-0 win at Augsburg, which took them two points clear of Bayern Munich with just one game to play. The Ivory Coast striker missed the first half of the season as he battled testicular cancer, returning in January.
Since Haller's return, Dortmund have lost just one of 18 league matches. "That he's back with us is a pure miracle" Terzic said after the game, praising the forward's "important" presence "in the dressing room".
Dortmund can seal their first title in a decade with a win at home against Mainz on Sunday and will also lift the trophy if they equal or better Bayern's result away at Cologne. The manager said the 28-year-old Haller scores "important goals" but "also lets the others next to him shine".