Chelsea completed the signing of Ross Barkley only days ago, bringing in the Everton midfielder for a bargain price of £15 million.

The move for the talented young Englishman is a smart piece of business from the powers that be at The Bridge – just as many of the club’s signings over recent years have been. Cesar Azpilicueta, Victor Moses, Cesc Fabregas and Eden Hazard – as well as a host more – have all been prime signings for the Blues in recent years, and represented good value for money.

However Chelsea have made their fair share of mistakes in the transfer window too, with a host of the club’s former stars going onto to big things since leaving South-West London. Which of these stars do you wish the club had kept hold of?

Kevin De Bruyne

Europe’s most outstanding midfielder. De Bruyne had two spells at Stamford Bridge, but was unable to nail down a first team position. He was subsequently sold to Wolfsburg, before returning to the Premier League with Manchester City in 2015. The Belgian looks on course to guide City to their third, and his first, Premier League title.

Mo Salah

Since leaving Chelsea as an unproven young signing from FC Basel, Mo Salah has set Europe, the world and most recently the Premier League alight. A brilliant spell with AS Roma earned Salah a return to England with Liverpool, for whom he has been the club’s stand-out player this season – bagging an impressive 23 goals this term already.

Ryan Bertrand

A surprise starter in Chelsea’s Champions League final victory over Bayern Munich in 2012, Ryan Bertrand never got the credit he deserved. Seen as the natural successor to Ashley Cole, things never quite materialised, however since moving to Southampton, Bertrand has established himself as England’s finest left-back.

Romelu Lukaku

Signed for £18 million as one of the continent’s hottest young strikers, loan deals at West Brom and Everton followed before being sold permanently to the Toffees after only four starts for the Blues. Now at Manchester United, Lukaku has scored 95 Premier League goals in just over 200 appearances. He’s still only 24.

Juan Mata

Not often do you get named a club’s Player of the Season before being sold the next summer – but that was exactly what happened to Juan Mata. The Spaniard was a fan favourite at Chelsea, but was un-favoured by former manager Jose Mourinho, and subsequently sold to Manchester United. Ironically, he is now re-united with the Portuguese at Old Trafford and is a regular starter for the Red Devils.

Who do you wish the club held on to?