|Full name||Sergio Alejandro Díaz|
|Date of birth||9 February 1985|
|Place of birth||Turón, Spain|
|Height||1.94 m (6 ft 4 in)|
|Playing position||Centre back|
|2003–2008||Real Madrid B||56||(2)|
|* Senior club appearances and goals counted for the domestic league only.
Sergio was born in Turón (Mieres), Asturias. After starting out at local Real Oviedo, making his professional debuts aged 17 in the second division in a relegation-ending season, he finished his football formation at Real Madrid, having joined in 2003.
During two seasons in the second level – of the five in total he spent with the team – Sergio amassed 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 (the group stage's last), but remained an unused substitute; he still earned another call, in La Liga against Sevilla FC, although he ultimately was cut from the final list of 18.
For the 2008–09 campaign Sergio joined Hércules CF, with the Alicante team being coached by his former Castilla boss Juan Carlos Mandiá. He appeared very rarely for the fourth-placed team in division two, following a severe injury contracted in preseason.
Sergio joined Gimnàstic de Tarragona for 2010–11, agreeing to a three-year contract with the second tier side. On 30 July 2011, however, he terminated his link with the Catalans, and returned to old club Hércules.
- Spain U17
- Sergio Díaz rescindeix el contracte amb el Nàstic (Sergio Días terminates contract with Nàstic); Gimnàstic's official website, 29 July 2011 (Catalan)