As part of his treatment, the striker has gone bald and has removed all of his facial hair.
He was diagnosed in July 2022, just a few weeks after moving to Dortmund, and has since undergone successful surgery.
“Sebastien Haller (28) will be absent from Borussia Dortmund for several months. The histological findings revealed a malignant testicular tumour. Haller, therefore, has to undergo chemotherapy treatment,” reads the club statement in July 2022.
Photos of the ex-Ajax striker and Ballon d’Or nominee’s new look circulated online, with some football fans wishing him well in his difficult situation.
Below are some reactions