#5 Ashley Cole

If selling to a title rival was not already highlighted as a frowned upon policy, Ashley Cole’s departure to Chelsea ends that argument. The talented full-back of England’s ‘Golden Generation’ left Arsenal in rather unceremonious circumstances considering he was an integral clog of the ‘Invincibles’ winning two Premier League titles and three FA Cups on the way.
More than a decade has passed, yet Arsenal have not been able to satisfactorily able to plug the hole. Cole went on to win seven major honours with Chelsea including a Champions League winner’s medal.
In the meanwhile, his understudies namely Gael Clichy, Kieran Gibbs, and Armand Traore have all tried unsuccessfully to nail the spot down for themselves. In the more recent past, Nacho Monreal and Sead Kolasinac have arrested the fall to some extent but Cole’s services both in defence as well as in attack have been missed.