Arsenal added to its depth in central defense with a player on course for a big future.
Arsenal have confirmed the signing of PAS Giannina defender and Greece under-21 international Konstantinos Mavropanos.
The 20-year-old made 20 appearances in all competitions after breaking into the Giannina team, scoring three goals.
"Young Greek defender Konstantinos Mavropanos has signed for us," Arsenal announced on their website.
"The 20 year-old centre-back arrives from PAS Giannina, where he has made 16 Greek Super League appearances since breaking into the first team last season.
"We’d like to welcome Konstantinos to the club and wish him well for the future."
The signing gives Gunners manager Arsene Wenger more options at centre-back, with Rob Holding and Calum Chambers starting alongside Shkodran Mustafi in Arsenal's 2-2 draw with Chelsea on Wednesday.
Laurent Koscielny and Nacho Monreal both missed the derby through injury, while Per Mertesacker was an unused substitute.
Mavropanos is one of the first signings made by Premier League clubs this January, coming after Liverpool completed a £75m deal for Virgil van Dijk and Leicester finally secured the signature of Adrien Silva.
Mavropanos spent eight years with Apollon Smyrnis before moving to Giannina who are currently 11th in the Super League, having won just three of their 15 games this season.