Dreyer previously played for Esbjerg fB, Brighton & Hove Albion, St Mirren, SC Heerenveen, Midtjylland, Rubin Kazan and Anderlecht.

[citation needed] Dreyer got his debut on 2 April 2017 in a 0–0 draw against Randers FC in the Danish Superliga[4] coming on in the 72nd minute to replace Awer Mabil.

[citation needed] In this season he finished as the league topscorer with 18 goals, helping Esbjerg win promotion to the Superliga.

[12] 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.

[16] 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.

[21] On January 22, 2025, it was confirmed that Dreyer had been sold to American MLS club San Diego FC on a three-year deal.