Esbjerg fB On 20 September 2016,
Esbjerg fB confirmed that they had extended Dreyer's contract by one year until 2018. But he continued playing for their U19 squad. Dreyer got his debut on 2 April 2017 in a 0–0 draw against
Randers FC in the
Danish Superliga coming on in the 72nd minute to replace
Awer Mabil. He scored his first goal for Esbjerg on 22 April 2017 against
AC Horsens. He was promoted to the first team squad for the 2017–18 season in the
Danish 1st Division. In this season he finished as the league topscorer with 18 goals, helping Esbjerg win promotion to the
Superliga. On 27 May 2018, Dreyer scored his first
hat-trick of his career in the second leg of their promotion playoff games against
Silkeborg IF. His 3 goals secured a 3–1 aggregate lead to take Esbjerg back into the Superliga. Dreyer ended the season as the topscorer
2017–18 Danish 1st Division, scoring 18 goals.
Brighton & Hove Albion On 7 August 2018, Dreyer was sold to
Brighton & Hove Albion. Dreyer started on the U23 team, and got his debut in the first game of the season against
Liverpool U23 on 8 October 2018. In January 2019, Dreyer joined
St Mirren on loan until the end of the season. After picking up an knee injury at the end of April, Dreyer returned to Brighton & Hove Albion and missed the end of the season. Dreyer scored one goal in his eleven appearances for the club. On 23 August 2019,
SC Heerenveen announced, that they had signed Dreyer on loan for the 2019–20 season. He made his debut 8 days later coming on as a substitute in a 1–1 home draw against
Fortuna Sittard.
FC Midtjylland On 6 January 2020,
FC Midtjylland announced that Dreyer had returned to Denmark and signed a four-and-a-half-year contract with the club. His strong start – two goals and one assist in his first two appearances for the club – led to him being named as the Danish Superliga Player of the Month for February 2020. On his debut on 13 September 2021 he scored a hat-trick against
Ural Yekaterinburg. He became the first player in the history of the league to score three goals in their first game in the league. On 11 March 2022, Dreyer's contract with Rubin was suspended until 30 June 2022 according to special FIFA regulations related to the
Russian invasion of Ukraine. The regulations allow foreign players in Russia to suspend their contracts until the end of the 2021–22 season and sign with a club outside of Russia until that date.
Return to Midtjylland On 16 March 2022, Dreyer returned to
FC Midtjylland on a loan until 30 June 2022. On 6 July 2022, he transferred to Midtjylland on a permanent basis and signed a four-year contract.
Anderlecht On 15 January 2023, Dreyer signed a four-and-a-half-year contract with
Anderlecht in Belgium.
San Diego FC On 22 January 2025, it was confirmed that Dreyer had been sold to American
MLS club
San Diego FC on a three-year deal. The club already had two of Dreyer's compatriots, namely
Jeppe Tverskov and
Marcus Ingvartsen. Dreyer made his debut for San Diego in the club's first-ever game, and subsequently scored the club's first-ever goal as part of a brace in a 2–0 win over reigning champions
LA Galaxy on 23 February. ==International career==