 A product of local CA Osasuna's youth system, Astiz was born in Pamplona, Navarre, and his earlier career was spent with the B-team where he met Jan Urban, a former club player who was manager of the reserves at the time.Thus, he was loaned for the 2007–08 season to Legia Warsaw (where Urban would work as coach) in the Ekstraklasa, becoming the first Spaniard ever to play in that competition.Astiz returned to Osasuna in June 2008, only to rejoin Legia immediately for five years despite still having a contract running.