#1 Nathan Ake (Bournemouth)

The Dutch international is a product of Chelsea's youth academy. He was given chance in Chelsea's first team but not on a consistent basis, thus in 2016, he was sold to Bournemouth. Ake is also capable of playing as a left back and sometimes he has been deployed as a midfielder as well.
Nathan Ake is a very composed player on the ball and he has shown great maturity on the ball as well. With Luiz likely to leave, Ake is a player who can definitely strengthen Chelsea's defense. His status as an academy player would also makes him popular among the fans as well.
Chelsea already have a buy clause inserted in his contract which they can activate till 2021. Given how difficult it is to sign quality players in the current transfer market, Chelsea have a great chance of signing a young player who can be very best in the future. Chelsea have been linked with a move to bring him back to Stamford Bridge as well.
For Nathan Ake, he was never really given a chance to impress at Stamford Bridge and he would want to make a mark at his boyhood club. He clearly has unfinished business with Chelsea.