6. Amaury Bischoff
You may think "who?" and this is one of the main reasons Amaury is #6 on this list. After signing from Werder Bremen in 2008 at the age of 22, Wenger had high hopes for the French-born, Portugal U21 international. Despite being injury prone, Wenger believed that Amaury would be worth the risk and made the "gamble on talent" as Arsene is quoted as saying. Bischoff made his first and only appearance for the Gunners ten months after signing and was released at the end of his one-year contract in June 2009. After his contract expiration, Amaury has played for two different Portuguese clubs and now plies his trade in the German third division for Preuen Münster. His meteoric fall is a sad one and, now at 26 years of age, it is doubtful that Bischoff will be able to go from German third tier football back to the level he was playing at under both Arsenal and Werder Bremen. Though injuries are at fault for this fall, he can still be deemed one of Wenger's poorest signings during his spell as Arsenal boss and what makes this signing even worse is the fact that Arsene knew of Amaury's injury record but still went through with the signing. Granted, it was low risk due to his lack of reputation and nonexistent transfer fee, but it was still a disappointing signing.
Transfer fee: Free transfer.