Dortmund is preparing for Guirassy move which would be really good to strengthen their scoring skills. However there are already 3 centre-forwards in the squad.
Serhou Guirassy should be the best signing Borussia Dortmund will accomplish as they prepare for the new season because the striker is a perfect match for their kind of football. He scored 30 goals in his 30 appearance for Stuttgart last season, a feat only achieved by top players. This is the reason he is the target of many clubs such as Atletico Madrid, AC Milan, Bayern Munic and also Borussia Dortmund. Although his present club is still interested in him as he still have 18 million Euros contract with them, the strike did not hide his interest in Borussia Dortmund in his recent interview at Sky SportOther than that Dortmund should work on signing some centre-backs too. Hummels is leaving and Niklas Süle has put on weight quite much recently. 
Hummels leaving Dortmund is a major source of concern for the team because he has contributed so much to the club and have also won the Bundesliga with the team for two seasons as well as other trophies. Well he has to go for the sake of continuity and the good thing being that he is leaving with honour.