Thomas Tuchel believes Kalidou Koulibaly can be Chelsea's next Thiago Silva

New Chelsea defender Kalidou Koulibaly has been handed a four-year deal because the club sees him as the next Thiago Silva.

The Blues hope to add two more top defenders in the shape of Sevilla Frenchman Jules Kounde and PSG star Presnel Kimpembe this week. But it was 31-year-old colossus Koulibaly, introduced pre-match, who excited fans at the Las Vegas Allegiant stadium here in Nevada on Saturday night.

The 31-year-old colossus has been handed a four-year deal at Stamford Bridge. He watched from the sidelines here as his new team eased to a 2-1 win over Club America. The length of his contract runs counter to the normal policy at Chelsea for players over 30. But Tuchel believes Koulibaly will match 37-year-old Silva in providing leadership, organization and quality deep into his thirties.

"It's nice that he takes the challenge right now," said the Blues boss. "And we have Thiago Silva, who is even older and super-experienced and still at the peak of his game. We hope Koulibaly can do the same and play for 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."

Silva was deemed surplus to requirements when he was allowed to join Chelsea for free two years ago. He went on to lead the west Londoners to the Champions League a year later, following up with the Club World Cup. He has also been to two FA Cup Finals and the League Cup Final.

Tuchel wants Koulibaly to emulate that kind of defensive consistency and longevity. "That's what we believe and that's what he is here for," added the German. "There were always rumors about him leaving Napoli but it was always super difficult - and in the end impossible - to get him because he was a key player."

Koulibaly was allowed to leave Napoli in this window because he had just a year left on his contract and was determined not to sign a new deal. The Italian club decided to cash in during this window instead of allowing the Senegal international to leave for free in a year's time.

Meanwhile Tuchel has urged rookie midfielder Conor Gallagher to build on his promising start to life in the first team squad after his impressive 45 minutes on Saturday. The 22-year-old spent last season on loan at Crystal Palace but made it clear to his parent boss at the end of the season that he wanted to play in the first team instead of going back to Selhurst Park.

"It was a very good start and a good match for him," Tuchel went on. "Now he must get used to our principles of the game, to understand when to move and when not to move. His work rate is outstanding and he has such a big heart. He can be a big asset for us."