Just a few weeks back, Chelsea were in contention for some of the best centre-backs in Europe as they strived to reinforce a position that has seemed unstable during the previous campaign.
The Blues suffered an uncharacteristic tenth placed finish last season after large spells of mediocre displays, during a campaign that also saw manager Jose Mourinho get sacked midway through the season.
Many of the poor results were largely owed to the shaky performances of the back four, with Branislav Ivanovic and Gary Cahill showing signs of declining sharpness and ability in defence, with the former being outplayed and simply outrun by opposition wingers at will.
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The long term injury to promising centre-back Kurt Zouma did not help the cause either, leaving the defence rather fragile and ripe for the picking.
Newly appointed manager Antonio Conte realises the urgent need to bring in one or two solid central defenders in order to provide some reassurance at the heart of the defence once again.
However, the west London outfit have experienced a few minor setbacks in their pursuit of quality centre-halves and seem to be ready to settle for lesser attractive options.
One of Chelsea's top summer targets was Juventus defender Leonardo Bonucci, with his performances for the Italian national team during Euro 2016 providing evidence of his immense quality.
Having played under Conte during their time together with The Old Lady, as well as the Azzurri, the 29-year-old understands the Italian manager's mentality and work ethic, a combination that could be fruitful at Stamford Bridge as well.
Unlike most centre-backs, Bonucci provides a calm presence at the back and has an impressive ability to carry the ball on his own as well as distribute it to advanced positions.
Possessing immaculate ball control and an uncanny ability to read the game, the Bianconeri defender is seen as a direct replacement for the aging John Terry.
However, Chelsea have been unable to lure the classy defender to Stamford Bridge so far, and with the likes of Manchester City and Manchester United also interested in his signature, it is looking more and more unlikely that a potential deal can be reached before the start of the new campaign.
Despite the fading hopes, Conte remains resolute in his pursuit of his former disciple, as the club are likely to continue the hunt for the defender till the end of the transfer window.
Kalidou Koulibaly is considered as one of the best central defenders in the Serie A, and is seen as the second choice option for the Blues in their chase for Bonucci.
Standing at six feet and five inches,the 25-year-old provides a powerful and solid presence at the back, possessing strong aerial abilities at the same time.
Understandably, Napoli are not eager to lose one of their key figures from last season and have already rejected a £19m bid from the Blues for their star defender. Despite the initial setback, Koulibaly's agent has confirmed that Conte is still in pursuit of the giant defender,reports the Sun.
It remains to be seen if Chelsea are successful in their attempts, especially due to the rising price of the Senegalese defender and the growing interest from clubs as such as Everton and Bayern Munich.
One of the main reasons for the Toffees going after the Napoli centre-back is the high possibility of their young and promising defender John Stones leaving for a potentially bigger club, Chelsea being one of them.
The Blues' pursuit of the England international seems to have suffered a blow, with City now considered the primary candidates to secure the 22-year-old's signature, especially due to the massive price tag attached to the player by the Merseyside club.
Another possible option for the Blues at centre-back is dynamic AS Roma defender Kostas Manolas.
The circling of other potential bidders for the Greek defender, as well as the Giallorosi's will to keep the player at the club, have not only seen the asking price for Manolas go up, but has made it extremely difficult for Chelsea to reach any sort of agreement for the defender.
Conte would be pleased if any of the aforementioned players joined the ranks at Stamford Bridge, which could take a lot of pressure off Terry and Cahill in central defence.
With Zouma set to be sidelined for a few more weeks, the Frenchman is likely to miss the start of the season.
Less experienced centre-backs such as Papy Djilobodji and Matt Miazga are not ready to feature regularly in the first team, making the need to find a suitable long term option in that position even more important.
Recent rumors have indicated that Chelsea seem to have given up on their pursuit for the likes of Koulibaly and Bonucci, and are willing to settle for lesser prominent individuals.
Benfica's Victor Lindelof is seen as a potential target for the Blues in a last ditch attempt to beef up the defence. The versatile Swede can operate at right-back and midfield as well, which could provide some added incentive to bring the 22-year-old to the club.
At such a young age, Lindelof could be a long term option for the west London club, but, it is certainly not the immediate answer to the club's defensive woes.
Perhaps the best backup defensive option, Valencia's Skhodran Mustafi, is seen as a possible target, with the German having impressed in the La Liga, as well as during Euro 2016 with the national side, also managing to score in their opening game against Ukraine.
With the club's pursuit of Bonucci drying out, Conte has diverted his attention to the 24-year-old German, who brings a good combination of experience and ability to the table.
Mustafi could therefore prove to be a decent addition to the Blues lineup.
However, failure to add either Bonucci, Koulibaly, or even Manolas, to the Blues back line would be considered a less than convincing piece of business with respect to the club's defence, especially as these players were the club's top priority before the start of the transfer window.
What defender should Chelsea be targeting this summer? Have YOUR say in the comment section below!