10. Alex Song
Kicking off this particular countdown is Cameroon international Song. The tenacious midfielder left Arsenal for Barcelona last summer and the Gunners were initially left far weaker by his absence.
Thankfully, the re-emergence of Welsh sensation Aaron Ramsey and the re-signing of combative Frenchman Mathieu Flamini has largely plugged the gap left by Song's departure - a move the player himself presumably now regrets after struggling to make any sort of real impact in La Liga.