4) Adrian Mutu (Parma to Chelsea – £17m)
The Romanian international had a pretty underwhelming first season at Stamford Bridge, scoring 10 goals in 36 appearances, but it was his ban for cocaine usage that made this a disastrous transfer.
Chelsea decided to release the forward during his seven-month ban, and they sued Mutu for compensation, which eventually led to the striker having to pay out €17m.