Early years and Mallorca

Born in Trinidad, Flores Department, Castro was a product of Club Nacional de Football's youth ranks. He made his professional debut on 13 July 2002 in a 3–1 win over Central Español, going on to become an important first-team member and helping them to two Uruguayan Primera División titles while finishing in the scorer charts' top three in the 2005–06 season.

On 7 August 2007, Castro signed a five-year contract with La Liga club RCD Mallorca.^[1] Rarely used in his first year, the same occurred in the 2008–09 campaign;^[2] however, during a week in March 2009, he managed to score in a 1–1 home draw against FC Barcelona in the Copa del Rey,^[3] adding a brace in a league 3–3 home draw with Real Betis after coming from the bench as the Balearic Islands team trailed 2–0 (and eventually 3–0).^[4]

In 2009–10, Castro finally beat competition from veteran Fernando Varela, starting most of the campaign and scoring six goals in 35 matches as Mallorca finished fifth and qualified for the UEFA Europa League (fourth until the last minute of the last matchday). On 23 October 2010 he netted twice at Valencia CF in a 2–1 victory, opening the score with a seventh-minute penalty kick;^[5] he scored five times in 33 games during that season, helping his team barely avoid relegation.^[2]

Real Sociedad

After leaving Mallorca in May 2012, Castro continued competing in the Spanish top flight, joining Real Sociedad for four years as a free agent.^[6] On 19 January 2013, he scored two of his six goals during the campaign^[7] to help the hosts come from behind 2–0 and defeat Barcelona 3–2.^[8]

Castro appeared in seven out of the Basques' eight matches in the 2013–14 edition of the UEFA Champions League – all rounds included – going scoreless in the process as the team exited in the group stage.^[9]

Málaga

On 6 January 2016, Castro terminated his link (which was about to expire) with Real Sociedad and moved to fellow top-tier side Málaga CF for two and a half seasons.^[10]