The 24-year-old Spanish midfielder was one of the star players for UE Cornella last season.
Medina - known as Agus - linked-up with Blues when they reported back for pre-season training.
He went on the Club's training camp in Portugal and started friendlies against Swindon Town and Reading.
Medina joined UE Cornella last summer after their Head Coach Xavi Calm - who now oversees Blues Under-23s - drafted him from Celta de Vigo.
He made 38 appearances and scored four times for UE Cornella, who reached the Segunda B Play-Offs.
Born in Barbera del Valles, Barcelona, central midfielder Medina came through Valencia's youth system before joining CE Sabadell FC.
From there he moved to Celta de Vigo's B side, where he spent two years, before the switch to Cornella.