Park Chu-Young
In fairness, when he arrived from Monaco for only £4 million, there was reason to believe that Park was actually a good bit of business.
The South Korea international had looked like a class act in Ligue 1—shimmying and shuffling his way through defences—he opted for Arsenal instead of Lille.
However, he was never truly trusted by Wenger and endured a succession of loan deals before leaving the club for Al-Shabab.