6) Gokhan Inler
Inler was a major transfer target for Arsenal back when he was still with Udinese, but he and his agent decided it was too early for him to move just yet.
He eventually made the switch to Napoli, and while he has enjoyed plenty of success in Serie A he could have gone on to be a major name in football; replacing the likes of Gilberto Silva, Aliaksandr Hleb, and Mathieu Flamini at Arsenal.