Chelsea manager Thomas Tuchel believes Kalidou Koulibaly will prove to be "another brilliant signing" for the Premier League club.
Koulibaly, 31, completed his move from Napoli to Chelsea last week in a deal reported to be worth £34 million ($40.6m), with the central defender signing a four-year contract. After a slow start to their summer recruitment, Chelsea completed two major signings in a matter of days, with England forward Raheem Sterling also arriving from Manchester City.
Koulibaly provides a much-needed boost to Chelsea's defence following the summer departures of Antonio Rudiger to Real Madrid and Andreas Christensen to Barcelona, both on free transfers.
Koulibaly revealed last week that he was close to joining Chelsea in 2016, and Tuchel said he is delighted to now have the Senegal captain as part of his squad.
"He brings experience, top defending quality, height, and everything we are looking for to play in a back-three or a back-four," the German told the Chelsea website. "It's another brilliant signing for us, and we hope Kalidou can show his quality as soon as possible."
Having spent much of his career in Naples - after coming through the ranks at Metz in France and a two-season spell in Belgian with Genk - Chelsea will be Koulibaly's first experience of England and the Premier League. However, Tuchel does not expect the defender to take too long to settle and will be helped by a couple of familiar faces.
"He knows already some of the players. He plays with Edouard Mendy with his national team and he played with Jorginho at Napoli," Tuchel said. "I think for this side it will be very quick that he feels welcome in the group. It's a nice group, and everybody is happy that he is with us now."
Under the previous ownership of Roman Abramovich, Chelsea had a strict rule that players over the age of 30 were only offered one-year contracts - the rule being broken only on rare occasions. Therefore the four-year contract signed by 31-year-old Koulibaly demonstrates a new policy under the new owners, and Tuchel is convinced the defender, who captained Senegal to the Africa Cup of Nations title in February, will justify the long-term deal.
"That's what we believe, and that's what he is here for," he said. "There were always rumours about him leaving Napoli. It was always super difficult and in the end impossible to get him because he was a key player there. It's nice that he takes the challenge right now.
"We have Thiago Silva who is even older and super experienced and still at the peak of his game, so we hope that Kalidou can do the same and play many years for us. He is totally fit and ready for the challenge, and he needs to be because we need him in top shape."
Chelsea opened their pre-season tour of the United States with a 2-1 win over Club America in Las Vegas on Saturday. Koulibaly and Sterling could make their first appearances for the Blues against London rivals Arsenal in the Florida Cup in Orlando this coming Saturday.