Transfer windows always keep the fans excited and interested as it is the time when fans can discuss, talk and enjoy the sense of belonging to their respective clubs. It is the time when fans discuss potential signings and choices of the club and players. The Premier League side Chelsea has been in the talks in most of the transfer windows due to some heavy signings and letting go some good players too.Chelsea has spent a lot of money in the past few years to get perfect replacements for many players. For e.g., after Ashley Cole’s departure, they have spent more than 100 million pounds on left backs and still they aren’t happy with the present options. Recent summer signing Alvaro Morata is now a huge concern for Conte and the board as Morata hasn’t been much consistent so far.With these continuous activities, Chelsea probably has made some mistakes in letting go some players who are shining elsewhere presently. These 5 players could have boosted the team and fans like us can’t ask for more. Chelsea and their fans will always regret letting go these players as they had all the potential in them and hence now are the stars in Premier League.Let us have a look at those 5 players:5. Ryan Bertrand (Left-Back)Current Club: SouthamptonAge: 28Current Value(Source: https://www.transfermarkt.com/ryan-bertrand/profil/spieler/40611): 20 Million EuroBertrand began his youth career at Gillingham before signing for Chelsea in 2005. He is a Chelsea graduate who was sent out on loan to various clubs. He made his Premier League debut on 20 April 2011 as he came in as a substitute for Ashley Cole and scored a goal. He was generally used as a backup option for Cole and was a good choice to play in that position. ?Chelsea v Blackburn Rovers – Premier League?Bertrand’s stay did not last for many years as he was again sent on a loan to Aston Villa in January 2014 and to Southampton in July 2014. He completed a permanent move to Southampton in 2015 and has been very impressive there. He is known as a perfect left back there as he has both the capabilities of attacking down the flanks and as well as defending and reclaiming possession. He has the tendency to make quick runs into the box and is tenacious in the tackle when defending. As compared to Marcos Alonso, Bertrand is much quicker in moving up and down the flanks and does not forget his defensive duties while making runs into the box. Alonso’s defensive performance has put up a question in Conte’s mind and hence he is looking to sign Alex Sandro from Juventus. Well, this situation could have been aborted if Chelsea did not permanently sell Bertrand. A huge amount of money and time would have been saved, as buying a new player now will take a considerable amount of time to settle in.