He began his career with Real Madrid but did not have any impact with its first team, and played for Mallorca and in England for West Bromwich Albion before joining Villarreal in 2010.

[3] Valero played only twice for the first team: given his debut by Fabio Capello against Écija on 25 October 2006, replacing Javi García after 60 minutes of a match in the Copa del Rey,[4] he also featured once in the UEFA Champions League, substituting Miguel Ángel Nieto in a 2–2 away draw with Dynamo Kyiv in the group stage.

[19] At the end of the campaign, Valero returned to his parent club after Mallorca confirmed they could not afford to take up the agreed fee of £2.5 million to make the move permanent.

[20] For 2010–11, it was reported that Valero was joining Villarreal on a five-year contract,[19] but the clubs eventually agreed on a season-long loan, with the move to be made permanent at the end of the campaign.

[21] He scored on his home debut, a 4–0 victory over Espanyol on 12 September 2010,[22] and featured heavily throughout the season as the team finished in fourth position and qualified for the Champions League.

[25] The move was confirmed three days later, and he joined the Serie A side alongside teammate Gonzalo Rodríguez;[26] he stated that leaving his previous club was not easy and that he still had not come to terms with its relegation.

He scored his first goal in 2013–14 on 15 September in a 1–1 home draw against Cagliari,[29] and, on 2 November, contributed to a 2–0 win at AC Milan;[30] subsequently, he was named in Goal.com's Serie A Team of the Season.

[37] On 30 June 2021, he announced his retirement from professional football,[38] but on 19 August confirmed to have agreed to join Florence-based fan-owned Promozione amateur club Lebowski.

[41][42] Primarily a central midfielder, Valero is a talented and creative playmaker, who is best known for his positional sense, vision, technique and passing ability,[43][44][45] as well as his leadership,[46] despite his lack of pace.