Chelsea are so keen on signing Alexander Isak from Newcastle United. They are willing to offer Nicolas Jackson in their bid to lower the £115million asking price. According to The Sun, the Blues want Isak to lead their attack next season under Enzo Maresca. Jackson endured a mixed debut season at Stamford Bridge after joining from Villarreal. Despite his struggles, Jackson managed to score 17 goals and provide six assists across all competitions. But it is understood that Chelsea are ready to send the Senegal striker to Newcastle if they can sign Isak. Isak finished last season with an impress…