#2 Romelu Lukaku
The big Belgian Romelu Lukaku, was one of the hottest young strikers on the planet when he was signed from Belgian club Anderlecht in 2011. He was highly anticipated to replace the ageing Didier Drogba up front with his strength, pace, and power, to serve him well in the physical Premier League.
He spent the majority of his first season playing for the reserves which was followed by a loan spell at West Brom for the entire 2012-13 season, where he gave a first-hand glimpse of his underlying potential. He scored 17 goals in the league outscoring his Chelsea teammates as well.
He returned to Chelsea the following summer when Mourinho returned to Chelsea. He missed the deciding penalty in 2013 UEFA Super Cup penalty shootout with Bayern Munich and later joined Everton on deadline day for another loan spell. He scored 15 goals for the Toffees in the league before returning back to Chelsea.
However, with no assurances from Mourinho regarding his role and future, Lukaku joined Everton permanently in July 2014 having made just 12 appearances for Chelsea and scoring zero goals.
At Everton, he has continued to thrive since then and has scored 66 goals so far across all competitions despite his young age.
In the same period, Chelsea bought Demba Ba, Andre Schurrle, Samuel Eto’o, Diego Costa, Loic Remy and re-signed Didier Drogba. Out of these attackers, only Costa has lived up to the expectations. Looking at the development of Lukaku over the last couple of years, everyone at Chelsea must be regretting letting the Belgian leave.