Born in Deba, Gipuzkoa,[2] and a product of Real Sociedad's youth academy, Riesgo made his professional debut with neighbouring SD Eibar in the Segunda División, 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.[3]
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.[4] 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,[5] 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.[6]
An undisputed starter throughout the season, Riesgo stopped two penalty kicks on 4 January 2009, helping league strugglers Recre to beat CD Numancia 3–1 at home.[7] 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 2–0 defeat at FC Barcelona;[8] the Andalusians eventually dropped down a level, with him appearing in all 38 fixtures.
On 18 June 2010, Riesgo – whose contract with Real Sociedad had expired – signed for Navarrese neighbours CA Osasuna for three years.[12] He acted solely as backup during his tenure with the club, first to Ricardo then Andrés Fernández.[13]
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.[14] On 2 September 2019, he joined second-division Girona FC for one year as a replacement for Sevilla FC-bound Bono.[15]
^Isasa, Xabier (30 August 2004). "Una Real incompleta" [Incomplete Real]. Mundo Deportivo (in Spanish). Retrieved 27 March 2014.
^Badallo, Óscar (28 September 2007). "Riesgo se pone 'Bravo'" [Riesgo gets all 'Brave' ("Bravo" in English)]. Marca (in Spanish). Retrieved 9 June 2016.