Borussia Dortmund on Monday completed the signing of Cologne striker Anthony Modeste as cover for Sébastien Haller, who is expected to be sidelined for several months after a removed testicular tumour turned out to be malignant. Haller was a headline signing from Ajax in summer but was diagnosed late last month before playing a competitive game for his new club. The much-travelled Modeste, 34, has now been secured as a back-up solution for a year after completing formalities in a move which was announced in principle on Sunday. “After our analysis of last season, we made a conscious decision t…