Sebastien Haller is set to undergo chemotherapy after being diagnosed with a malignant testicular tumour.   The 28-year-old striker who joined Borussia Dortmund in July for £27million from Ajax,   On Saturday, July 30, the German club confirmed that the Ivory Coast international would undergo treatment for several months, but insisted that striker had a ‘very good chance’ of recovery.   Haller was diagnosed with a testicular tumour earlier this month and underwent surgery a few days ago, after complaining …