Chelsea are close to completing the signing of Senegalese defender Kalidou Koulibaly from Napoli. As reported by Football.London, the 31-year-old has signed a contract and completed his medicals ahead of his move to Stamford Bridge.Koulibaly is set to become the Blues' second summer signing after they completed the signing of forward Raheem Sterling from Manchester City.LDN@LDNFootbalI Fee agreed (£33m) Personal terms agreed (4 year deal) Medical passed See you soon, Kalidou Koulibaly… 11293879✅ Fee agreed (£33m)✅ Personal terms agreed (4 year deal)✅ Medical passed See you soon, Kalidou Koulibaly… 💙 https://t.co/sGzEwtzuBuThe recruitment of at least two centre-backs has become a top priority for coach Thomas Tuchel this summer following two crucial departures. Antonio Rudiger and Andreas Christensen moved to Real Madrid and Barcelona respectively after the expiration of their contracts with the Blues.The Senegalese defender is one of the most highly-rated centre-backs in Europe. His experience and expertise will give the West Londoners the needed stability at the heart of their defense.Like every new arrival, the question "What jersey number will Koulibaly wear at Chelsea?" arises. This article will take a look at three possible jersey numbers the Blues could allocate to the Senegalese.#3 Number 26SSC Napoli v Cagliari Calcio - Serie AOne possible jersey number for Koulibaly is No. 26. This is the number the Senegal captain has been wearing at club level ever since he joined Napoli from Genk eight years ago.The jersey number is currently vacant at Stamford Bridge and hasn't been worn by any player since the 2016-17 season. The last player to sport the No. 26 was Blues legend and centre-back John Terry.Mbabazane@uMavestaSo Koulibaly is gonna wear jersey number 26? At Chelsea? #CFC1So Koulibaly is gonna wear jersey number 26? At Chelsea? 👀 #CFCIt is unknown if the number was officially retired in honor of the former Chelsea skipper. If it wasn't retired, it means that the Senegalese defender could very well be the next wearer of the honorary number.#2 Number 4US Sassuolo v SSC Napoli - Serie AJersey No. 4 is another possible number that could be allocated to the 31-year-old centre-back. The jersey No. 4 became vacant following Christensen's exit from the club this summer.The Blues have allocated this number to centre-backs in the past. Before Christensen, a certain David Luiz wore the number during his first stint at the club in 2010-11.No. 4 is one of the ideal squad numbers for a defender and the Senegalese could opt for it.#1 Number 2SSC Napoli v FC Barcelona: UEFA Europa LeagueAnother possible ideal number for Chelsea's in-bound defender is jersey No. 2, which became vacant after Rudiger left the club for Real Madrid.The Senegalese is being recruited as a direct replacement for the German defender. Both players have similar defensive qualities and Chelsea could outrightly allocate the No. 2 jersey to their latest centre-back.Koulibaly is expected to be a first-team regular at Chelsea, thus making this squad number the best possible option for a starting center defender.