Number 1. Diego Forlan
Known mostly for going off during the 2010 World Cup, Diego Forlan could not find a way to transfer that talent to his stint in Manchester United from 2002-2004.
Signed for £6.9 million in January of 2002, he could not live up to the hype of the fans, and the club. Scoring an impressive 37 goals with his former club, Independiente, in just 80 appearances, he was expected to thrive at Manchester.
After 63 appearances, he only scored 10 goals, and was transferred two seasons after being signed. With Villareal, he scored 54 goals in 106 appearances, a much better goal to game ratio than what he had at United.