 Born in Vélez-Málaga, Andalusia, Hierro started playing professionally with local CD Málaga, but only appeared in a combined 26 games for the first team in his first five seasons, also suffering La Liga relegation in the last one.After one more year in Segunda División, he signed with Real Valladolid of the top level.After helping the Castile and León side finish eighth in his second season, with one of the best defensive records in the competition (38 matches, 34 goals), Hierro signed with FC Barcelona, but only lasted a few months in Catalonia, moving to Real Betis on loan.