Arsenal sporting director Edu must learn lessons from the club’s past when it comes to offloading one player this summer. Arsenal have not always been the most successful club when it comes to selling players. In recent years, the Gunners have allowed the likes of Mesut Ozil, Pierre-Emerick Aubameyang, Nicolas Pepe, Hector Bellerin, Alexandre Lacazette, and Aaron Ramsey, amongst others, to leave for nothing. When they have fetched a fee, it has also often been lower than many would have expected. Following his best ever season at the Emirates Stadium, Arsenal received just £21 million for Gran…