Sergio Alejandro Díaz (born 9 February 1985) is a Spanish retired footballer who played as a central defender.

[1] Over two seasons in the second division – of the five in total he spent with the team[2]– Díaz made a further seven league appearances with the reserves.

He was also called up to the first team for a UEFA Champions League match against FC Dynamo Kyiv in December 2006 (the group stage's last), but remained an unused substitute;[3] he earned another call that month, in La Liga against Sevilla FC, although he ultimately was cut from the final squad of 18.

[4] For the 2008–09 campaign, Díaz signed with Hércules CF, who was coached by his former Castilla manager Juan Carlos Mandiá.

[5] Díaz moved to Gimnàstic de Tarragona in 2010–11, agreeing to a three-year deal with the second tier side.