Sérgio Miguel Relvas de Oliveira CvIH[2] (born 2 June 1992) is a Portuguese professional footballer who plays as a central midfielder for Super League Greece club Olympiacos.

On 17 October 2009, he became the club's youngest ever player to appear for the first team, at the age of 17 years, four months and 15 days, in a 4–0 home win against Sertanense in the third round of the Taça de Portugal; during the game, he provided an assist for Hulk in one of the goals.

[6] In the summer of 2011, still owned by Porto, Oliveira was deemed surplus to requirements by new manager Vítor Pereira as practically all Portuguese players, and joined Belgian Pro League club Mechelen.

[15][16][17][18] After having been sold back to Porto before the start of the 2015–16 campaign,[11] Oliveira scored his first competitive goal for the side on 3 February 2016, helping to a 3–0 away defeat of Gil Vicente in the semi-finals of the domestic cup.

[22] His importance grew even further as he spent the final stretch of the season as a starter, forming a revamped midfield partnership with Héctor Herrera after Danilo Pereira suffered a serious injury which ruled him out for several months.

[36][37][38] On 9 March 2021, he scored a brace in a 3–2 loss after extra-time to Juventus in the Champions League round of 16 – an early penalty and a 115th-minute free kick – to qualify his team on the away goals rule.

[41] As the summer transfer window closed, no moves materialised, and he began the 2021–22 season on the bench, as fellow youth graduate Bruno Costa who had just been re-signed started in his place.

[47] He made six appearances as the Giallorossi won the inaugural edition of the UEFA Europa Conference League, and scored the only goal in the last-16 first leg away to Vitesse in which he was also sent off;[48] he replaced the injured Henrikh Mkhitaryan after a quarter of an hour in the final on 25 May in another single-goal win over a Dutch side, Feyenoord.

[51] His first goal came on 16 September to open a 2–1 home victory over Konyaspor in 59 seconds;[52] he won the domestic league in his first season, confirming it with two games to spare in a 4–1 away defeat of Ankaragücü where he scored.

[56] Oliveira was selected by the Portugal under-19 team for the 2010 UEFA European Championship; in the tournament in France, he scored in a 2–0 group stage victory over Italy[57] as both nations went on to be eliminated after the first three games.

[62] He won his first cap on 6 September of that year, replacing William Carvalho for the final ten minutes of a 1–1 friendly draw with Croatia in São João da Venda, Algarve.