Kalidou Koulibaly joins Chelsea in second summer transfer after Raheem Sterling

Kalidou Koulibaly has become Chelsea's second summer signing after flying out to the US to meet up with his new team-mates.

Koulibaly has joined the Blues on a four-year contract after Napoli agreed to a £33.8million (€40m) deal for the 31-year-old. He follows Raheem Sterling, who has already joined in a £50m deal from Manchester City. The Senegal international underwent a medical in London on Thursday and has now flown out to Las Vegas to join up with Thomas Tuchel and his squad, who are preparing to play Mexican side Club America on Sunday.

He will reinforce the centre of Chelsea 's defence following the significant losses of Antonio Rudiger and Andreas Christensen, who left on free transfers to join Real Madrid and Barcelona respectively. Koulibaly arrives at Stamford Bridge with lots of experience, having made 317 appearances for Napoli since a £6.5m move from Belgian side Genk in 2014.

Speaking after his arrival, Koulibaly said: "I'm very happy to be here with this team at Chelsea, it's a big team in the world and my dream was always to play in the Premier League. Chelsea came first to get me in 2016 but we didn't make it. Now when they came to me I accepted it because they really wanted me to come to the Premier League to play for them.

"When I spoke to my good friends Edou and Jorginho they made my choice easier so I'm really happy to be with you today. I want to thank the fans because I saw a lot of them in London and on the plane everybody was happy for me to be here. So I want to thank them and I hope the season will be really good and we will give some good moments to the fans.'

Koulibaly had himself already confirmed his departure from Napoli on Friday in an emotional Instagram post. He wrote: "My two children were born in Naples. I have met people who will forever be part of my life and who made me and my family feel at home: from the first to the last moment. Thanks to you, Naples, I became the man I am today.

"Thanks to the club, the President, the coaches, all my teammates and all the people I have had the pleasure of working with over the years. Thank you, Naples and Neapolitans, for all the love we have given each other.

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"I am proud to have honoured you with all of myself and I will continue, indefinitely, to carry you in my heart and to nurture one of the most important feelings for me: respect. You have been everything for me. Now I feel I have to leave and get back into the game: it's time for a new adventure."

Koulibaly won't be the only centre-back arriving at Chelsea this summer, with Tuchel wanting at least two to bolster his depleted options amid the possibility Cesar Azpilicueta could be allowed to leave for Barcelona. "We need some centre-backs - at least two to replace Andreas and Toni," he said on Friday. "We have Azpi at the moment in our squad, and we plan with him, but there are talks going on about his personal situation and what we want. We will be very open with you, so that makes it three.

"I think with Thiago [Silva] in the middle, Toni on the left, and Azpi or Andreas (on the right), we had the best back three in the world. Not a lot of teams play with a back three, but this was a fantastic back three. Trevoh [Chalobah] then stepped up and played a huge role. He needs to improve, and he will get the responsibility. Hopefully, he takes that. But still, we need a deep squad. Otherwise, we will not compete."