Chelsea have completed a deal for teenage defender Mamadou Sarr from Ligue 1 club RC Strasbourg.
The 19-year-old has signed a contract until 2033.
Sarr, a France U20 international, played a key role in Strasbourg securing qualification for Europe next season, making 28 appearances across all competitions.
A statement released on Chelsea's official website read on Monday read: "Welcome to Chelsea, Mamadou!"
The Blues have already been busy during this window, completing deals for midfielder Dario Essugo from Sporting Lisbon, Estevao from Palmeira and striker Liam Delap from Ipswich.
The west Londoners are set for more activity in the weeks ahead, with interest in AC Milan goalkeeper Mike Maignan, among others.
Sarr's move enables him to take part in the upcoming Club World Cup in the United States, with Chelsea's campaign beginning against LAFC on June 16.
Chelsea's initial offer of €35m (£29.5m) for Jamie Gittens has been rejected by Borussia Dortmund, according to Sky in Germany.
Negotiations are ongoing between the parties and a new bid from Chelsea is expected.
Dortmund are understood to want €50-60m (£42-50m) for the forward.
The England U21 international wants to join the Blues and play for them in the Club World Cup.
Chelsea are looking to strengthen in the winger position following the decision not to take up the option to sign Jadon Sancho permanently.
