Born in Deba, Gipuzkoa, and a product of Real Sociedad's youth academy, Riesgo made his professional debut with neighbouring SD Eibar in the second division, where he would play for one and a half seasons. In March 2004, he was recalled from his loan due to an injury to first-choice Sander Westerveld. After Westerveld was waived in the summer, Riesgo became a starter for the Basques, making his La Liga debut on 29 August 2004 in a 1–1 home draw against Levante UD. From the 2006–07 campaign onwards he battled with newly signed Claudio Bravo for starting duties; with the Chilean as the first-choice, Real were relegated. In 2007–08, however, Riesgo played all 42 league matches, although the team did not achieve a top flight return. In August 2008 he was loaned to Recreativo de Huelva for €350.000, with the club having the option to make the move permanent afterwards for €4.3 million and not having to pay the player's wages. An undisputed starter throughout the season, Riesgo stopped two penalty kicks on 4 January 2009, helping league strugglers Recre beat CD Numancia 3–1 at home. On 11 April he became the first to ever deny Lionel Messi a penalty, clawing the Argentine's effort out of the air as he saw his side bow down to a 0–2 defeat at FC Barcelona; the Andalusians eventually dropped down a level, with him appearing in all 38 fixtures. In December 2009, Riesgo served a trial at Premier League side Tottenham Hotspur as potential cover for injured Carlo Cudicini, lost for the campaign after a motorcycle accident. Upon his return, he found himself third-choice at Real Sociedad behind Bravo and Eñaut Zubikarai, totalling only 630 minutes of play as they returned to the top level after three years. On 18 June 2010, Riesgo – whose contract with Real Sociedad had expired – signed for Navarrese neighbours CA Osasuna, for three years. He acted solely as backup during his tenure with the club, first to Ricardo then Andrés Fernández. Riesgo returned to Eibar in the 2015 off-season after agreeing to a one-year deal, as the team was now in the top flight. On 2 September 2019, he joined second level's Girona FC for one year as a replacement for Sevilla FC-bound Bono.
