[9] Almost exclusively a substitute in his first season, he scored once for his first goal in the league on 17 September, at the end of a 1–2 home defeat to eventual champions FC Porto.

[11] On 17 June 2020, he was one of three players in his team to be sent off in a 2–1 home loss to Benfica – for a high foot on Pizzi – and was subjected to social media abuse by his club's fans.

[17][18] He contributed four goals in 2,073 minutes in 2023–24 to another league title,[19] but missed the vast majority of the following campaign after rupturing the tendon of his right knee;[20] in November 2024, he was handed an eight-match suspension for smashing a glass protection while in the stands – he was not part of the squad due to injury – and injuring two spectators (one of them seriously) during the 4–3 loss against Porto in the Supertaça Cândido de Oliveira in August but, controversially, the ban was to be served while he recovered.

[21][22] Santos was part of the Portugal squad at the 2015 FIFA U-20 World Cup, scoring an early goal against Senegal (3–0)[23] and a late one against Colombia (3–1 win) in the group stage,[24] in an eventual quarter-final exit in New Zealand.

He won the first of his two caps for the under-21 side on 12 November of that year, replacing Rony Lopes midway through the second half of the 4–0 victory over Albania for the 2017 UEFA European Championship qualifiers held in Arouca.