Highly-rated German teenage defender Karim Coulibaly has penned a five-year deal with Strasbourg after joining from Werder Bremen, the Ligue 1 club confirmed on Friday.
The deal for the 19-year-old, who came through Hamburg's youth side, is worth 20 million euros ($23 million), according to a source close to the negotiations.
Coulibaly played 27 matches last season and helped Bremen stay in the Bundesliga.
He is the most expensive signing of Strasbourg's transfer window as the club that is part of the BlueCo group that owns Chelsea have recruited several promising young players.
On Wednesday, Strasbourg announced the arrival of Costa Rican international defender Jeyland Mitchell, 21, from Austrian club Sturm Graz.
Strasbourg have seen several key departures this summer, including Paraguay's World Cup star Julio Enciso and Ivorian Abdoul Ouattara to Premier League club Ipswich as well as Belgian international Diego Moreira, who moved to AC Milan.
The club were fined 13 million euros by UEFA in June for breaching Financial Fair Play regulations.
