Born in Pamplona, López Vallejo began his career at hometown's CA Osasuna, making his first appearance for the main squad not yet 19 in a 3–0 home win over Sporting de Gijón on 15 May 1994, although the Navarrese had already been relegated from La Liga.

[2] López Vallejo signed for Villarreal CF in 1999 alongside teammate Jesús Unanua (also a goalkeeper), appearing in all the games during the 1999–2000 campaign as the club returned to the top flight after a one-year absence.

[3] With the signing of Pepe Reina in 2002 and the subsequent arrival of imports Sebastián Viera and Mariano Barbosa, however, López Vallejo was consecutively demoted to backup and third-choice.

[5] As the latter moved to Tottenham Hotspur in August 2008 he became the starter, with the side now in the Segunda División, and was instrumental as they immediately returned to the top tier.

[8] However, he lost his position in January 2010 with the arrival of new coach José Aurelio Gay and, later that month, was released by mutual consent;[9] he immediately found a new team, joining Levadiakos F.C.