#6 Yaya Sanogo

The French youth international striker joined from Auxerre as a free agent after his contract with the Ligue 2 outfit expired. Sanogo came up through the youth ranks of Auxerre and made 21 senior team appearances for the French side, scoring on 11 occasions.
His performances in the Fifa Under-20 World Cup in Turkey caught the attention of Wenger and his trademark policy of signing promising but unproven players continued with Yaya Sanogo.
However, Wenger’s gamble did not pay off. Blessed with pace and strength, Sanogo made 20 appearances for the Gunners. Wenger soon realized the kid was not yet ready and sent him out on loan to Crystal Palace, Ajax, and Charlton Athletic.
Sanogo finally left Arsenal in 2017 to play for Ligue 1 side, Toulouse. Though he has age on his side, it is unlikely, Sanogo will see top-flight English football again in his career.
#7 Amaury Bischoff

Another bargain that backfired. In the summer of 2008, Arsenal lost some key players in midfield - Gilberto Silva was sold to Panathinaikos, Alexander Hleb left for Barcelona and Mathieu Flamini left on a free transfer to AC Milan.
Wenger felt he needed to add a midfielder to his squad. He decided to gamble on the French-born Portuguese Under-21 international. Signed from Werder Bremen on a free transfer, Bischoff was never good enough for Arsenal.
Bischoff initially appeared for Arsenal’s reserve side but found it difficult to break into the senior team. Bischoff’s only appearance in the Premier League came against Portsmouth towards the end of the 2008/09 season, replacing Theo Walcott in the 64th minute. He was released by the club after just one season and he never came back to the top level again.
Currently 31, Bischoff plays for Hansa Rostock in the third tier of German football.