 Born in Catoira, Pontevedra, Sergio began his career with local Arosa SC, joining Galician neighbours RC Celta de Vigo in 1999 at the age of 13.He made his senior debuts with the B-side in Segunda División B, playing four full seasons in the category and spending 2008–09 on loan to another club in that level and region, Racing de Ferrol.Sergio made his debut for Celta's first team on 4 June 2011, in a 3–0 Segunda División home win against FC Cartagena, the last matchday of the campaign.