Midfielder- Nemanja Matic
Matic was another man who moved on to Manchester United when his time at Chelsea came to an end, but unlike Mata, he followed Mourinho to Old Trafford. The Serbian midfielder actually had two spells with the Blues. The first ended when he moved to Benfica as part of an exchange to bring David Luiz to Chelsea. His second spell was much more successful, as he was involved in two Premier League title-winning sides, before being reunited with his former manager at United.
Midfielder- Kevin de Bruyne
Of all the players Chelsea have sold over the years, they will regret none more than the sale of de Bruyne. They signed the Belgian from Genk in 2012 but sent him out for a season on loan at Werder Bremen, where he first began to show the signs of being a top player. However, after becoming frustrated with a lack of first team action, he left Chelsea and moved to German side Wolfsburg. He later moved on to Manchester City, where he established himself as one of the top midfielders in world football.