#1 Adrian Mutu

The likes of Shevchenko and Torres might’ve cost Chelsea more money than Romanian striker Adrian Mutu – who arrived at Stamford Bridge in the summer of 2003 from Parma for a fee of £15.8m – but no other Blues signing can match Mutu for sheer unprofessionalism during his time at the club. Simply put, the way his Chelsea career ended makes him by far their worst ever signing.
Things actually started well enough for the Romanian; as one of Roman Abramovich’s first-ever signings, the pressure was on for him to succeed and he started off quickly, scoring 4 goals in his opening 3 games including a winner against Leicester and a brace against Tottenham. 10 goals in 36 appearances across all competitions in 2003/04 wasn’t the best return, but it did seem like the best was yet to come from the striker.
That was proven wildly wrong in his next season, though. Mutu fell out with new boss Jose Mourinho almost immediately, accusing the Portuguese of lying that he was injured in order to prevent him from playing for Romania in a World Cup qualifier. Shortly after, his Chelsea career came to an abrupt end when he tested positive for cocaine – and was subsequently banned from football for 7 months.
The issue caused such a scandal that Chelsea ended up firing the Romanian – who moved back to Italy with Juventus – and eventually decided to take him to court for breach of contract following the positive test.
After years of legal proceedings, Mutu was forced to pay Chelsea £17m. The money recouped his transfer fee but still doesn’t change the fact that due to his unprofessional behaviour, he remains the Blues’ worst-ever signing.