Strikers - Diego Costa (Atletico Madrid) and Romelu Lukaku (Manchester United)
Chelsea signed Diego Costa ahead of the 2014/15 season by paying the £32m buy-out clause in his contract. The Brazil-born Spain international scored 59 goals in 120 games for Chelsea and played a crucial role in winning the Premier League twice.
Costa fell out with Antonio Conte and that resulted in him being frozen out of the squad before the 2017/18 season. The 29-year-old returned to Atletico Madrid in January 2018 and helped them win the Europa League.
Romelu Lukaku joined Chelsea in 2011 aged 18 from Anderlecht and before he joined Chelsea, he already scored 41 goals in 98 games for the Belgian giants.
Lukaku only played 15 games for the Blues and never scored a goal for them. However, during his time with Chelsea, he went on loan to West Brom and Everton scoring 33 goals in 71 games before eventually joining the latter on a permanent deal.
Lukaku scored 87 times in 166 games for Everton in four seasons before making a £75m move to Manchester United in the summer of 2017 even though there was interest from Chelsea to resign the player.
Honourable mentions - Daniel Sturridge (Liverpool), Samuel Eto’o (Free agent), Fernando Torres (Sagan Tosu) and Dominic Solanke (Liverpool)