Six months after Haller was diagnosed with testicular cancer, during a medical examination, he was back on the football field.
During the fall, the 28-year-old striker underwent two operations and four rounds of chemotherapy.
After being declared healthy from cancer, he has been back in training in recent weeks.
When Dortmund played a training match against Fortuna Düsseldorf, Haller jumped in in the 74th minute.
Dortmund won the match 5–1.
The Ivorian came before the season to the German club from Ajax, where he was involved in taking home the domestic shooting league.