Chelsea have signed teenage French midfielder Lesley Ugochukwu from Rennes on a seven-year deal for 27m euros (£23.2m).
Ugochukwu, 19, has made 47 Ligue 1 appearances for Rennes and has also featured in the Europa League.
He is yet to make his senior debut for France but has played for Les Bleus at under-17, under-18 and under-19 levels.
His arrival comes after Chelsea boss Mauricio Pochettino recently said the Blues needed to add to their midfield.
The BBC understands Ugochukwu, who made his senior Rennes debut just after his 17th birthday, could be sent back out on loan to Ligue 1 side Strasbourg.
Chelsea have a plan to sign young talent that have potential to be future stars of world football, while clearing out their bloated squad following a £600m spend in the past two transfer windows.
Ugocukwu’s deal also has the option for another year.
Chelsea’s co-sporting directors Laurence Stewart and Paul Winstanley said: “He [Ugochukwu] is an impressive young player who has already made his mark in Ligue 1. He has a huge amount of potential and we know he is going to continue to develop and improve.
“We are pleased that he has joined us in the United States [on their pre-season tour] and that he will be able to integrate with the squad quickly.”
Kai Havertz, Mateo Kovacic and Mason Mount have all departed the club this summer for Arsenal, Manchester City and Manchester United respectively, while N’Golo Kante, Kalidou Koulibaly and Edouard Mendy have moved to the Saudi Pro League.
Ruben Loftus-Cheek and Christian Pulisic both made the switch to Italian giants AC Milan.
The Blues are reportedly pursuing a deal for Brighton midfielder Moises Caicedo, while Conor Gallagher has been the subject of a £40m offer from West Ham.
Chelsea have already added attackers Christopher Nkunku and Nicolas Jackson to their squad as well as Brazilian youngster Angelo Gabriel.
Source: BBC Sport