David Luiz joined Chelsea for a second spell in the summer of 2016. He went on to win the Premier League and a FA Cup with the club so far. He did reveal this year that had Antonio Conte stayed in charge he would have left the club.
Under Maurizio Sarri he has a new lease of life were he became a regular starter for the club. But it is clear that the trust Sarri he has not been awarded for that. The Brazilian has been largely inconsistent for the Blues.
In some games such as the one at home to Manchester City, the former PSG defender was rock solid, but apart from that, we have hardly seen a solid display from David Luiz. Despite this, the club is ready to offer him a new contract with one-year extension. But the Brazilian has rejected the offer and wants a new deal for a longer term.
The Blues have a policy of not offering a contract of more than one year to a player over 30 and the former Benfica defender is 31 now. The kind of performances he has given this season are not definitely not enough to convince Chelsea to break their policy and it seems like they would be happy to let him leave for free.
If he leaves they will have enter the market for a new defender, here are five defenders Chelsea should target to replace David Luiz-
#5 Kalidou Koulibaly (Napoli)

Though the acquisition of the former Genk defender will definitely be expensive and it will require Chelsea to break all sorts of transfer records. But considering the performances he has given for Napoli over the years, he should be worth the money.
The Napoli defender is 6'4 in height, physically strong and he is quick as well. His strong presence at the back will give Chelsea a reliable defender compared to David Luiz. The Senegalese is only 26 years old and unlike David Luiz, he has shown that he can deliver good performances consistently.
Chelsea have been linked with a move for him, but a move never really materialized. But considering how badly they have been conceding goals, it would wise for Chelsea to spend big on a centre back like him. Manchester United and FC Barcelona also have been linked with a move for him.
While for Koulibaly, at Napoli he has only won an Italian Super cup while at Chelsea he will have the chance to challenge for major honours and big trophies every season.
#4 Alessio Romagnoli (AC Milan)

The AC Milan captain has been one of the best performers for the Rossoneri. At the age of 23, he has shown great maturity and leadership skills. The Italian is the product of the AC Milan youth academy and he has been one of the best defenders in Serie A.
The departure of big-name players or leaders like John Terry has left a huge void in Chelsea's dressing room. Romagnoli is a natural leader like John Terry and currently, Chelsea need players like him in their squad who can not only lead by words but by actions as well.
Milan could consider selling due to their financial problems. Now, with Bakayoko on loan at Milan Chelsea could use him to land the Italian. The Blues must also consider how difficult it is to sign quality players in today's market and such a deal would be beneficial for both the teams.
Though AC Milan have put in a lot of efforts to reach back to their former glory but still nothing is guaranteed for them. While at Chelsea trophies are a guarantee every season and Romagnoli might be tempted to move to away from the troubles at San Siro.
#3 Harry Maguire (Leicester City)

The Leicester City defender has already shown at the World Cup that he is capable of producing good performances at the biggest stage in World football. At the age of 25 Harry has a lot of years of peak left in him.
Like Luiz, Harry prefers to play on the left side of the defence. The Englishman has shown a lot of composure on the ball, unlike David Luiz who still makes rash decisions. Like Luiz Maguire also likes to come out the ball and he is very good at doing so and at the same time he good at defending as well.
Maguire is a homegrown player which means that if Chelsea sign him it won't come under UEFA Finacial Fair Play. Also, Chelsea need quality English players in their squad and given that Leicester City is a selling club, the Blues could use their financial muscle to bring Maguire to Stamford Bridge.
The former Hull defender is capable of big things and at Leicester, it is highly unlikely that he will reach his potential and make a big name for himself in world football. Thus, a move away from the Foxes to a big club would be in the best interest of Maguire.
#2 Kostas Manolas (AS Roma)

The Greek international has been one of the most consistent defenders in Serie A since his arrival at AS Roma. He also has good of experience of playing European football as well and he is only 27 years old.
The former Olympiacos defender has good physical strength and at the same time, he also has the speed to match quick attackers. While David Luiz clearly lacks the speed and concentration, Monolas on other hand has good concentration and alertness, which is necessary for a defender.
He has been linked with a move to Chelsea in the past but this summer Chelsea are clearly looking to overhaul their squad and the Greek defender should be a target for them, as his contract with Roma contains a release clause as well. Manchester United are also interested in bringing him to Old Trafford.
Monolas has the quality to be considered among the best defenders in the world, but the fact that AS Roma are not ambitious could make him consider to leave the Italian capital to a place where he can be considered among the best defenders in the world.
#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.