Walgreen reports its latest quarterly results next week and Jim Cramer believes it will be a key item to watch. After CVS Health and Rite Aid both reported blowout quarters, if Walgreen doesn't do the same, the stock may sell off. Cramer says that will present an opportunity for investors. Looking ahead to 2015, Cramer says Walgreen will become more international, with less costs and less impacted by the 'drugstore wars' that take place in the United States when it completes its merger with Alliance Boots. And while Cramer says he likes president and chief executive Greg Wasson, he notes that many people believe a leader at the helm with a more global perspective will be able to take Walgreen higher. He advises investors use any weakness in the stock to buy.