4. Xabi Alonso
Arsenal were strongly in for Xabi Alonso at the start of the 2008/09 season, and supposedly could have had him for just slightly over £18million. With Alonso then moving to Real Madrid for £30million the following season, that looks like an opportunity for a real bargain missed again by the Gunners. The Spaniard would have fitted in perfectly into Arsenal’s style of play, forming a great partnership with fellow countryman Cesc Fabregas, who at the time had to make do with playing alongside the likes of Abou Diaby, Denilson and even Emmanuel Eboue on occasion. Undoubtedly one of the best midfield playmakers of the Premier League in recent years, a very bad decision by Arsenal not to bid slightly higher.