Predominantly a central midfielder, Fisker started his career at local Superliga-side Randers FC before spending two seasons at Skive IK, first on loan and since on a permanent deal.

Fisker returned to Randers in January 2014, playing three years for his childhood club before moving to Brøndby IF in 2017 where he won the Danish Cup in his first season.

[3] He made his debut against Vejle Boldklub two years later,[4] before moving to Skive IK on loan in July 2007, having played only the one match for the first team in Randers.

[17] He had a strong finish to his career in the club, helping Hobro to first place in the table by the winter break, while personally winning 1st Division Player of the Year for 2013.

[22] In March 2015, Fisker signed four-year contract extension with Randers and stated that he hoped to continue playing top-flight football for the club for years to come.

[24][25] Fisker missed the start of the 2015–16 season and his European debut against Andorran side UE Sant Julià due to a pulled calf muscle.

Fisker finished the season with 38 total appearances in which he scored two goals, as Randers ended seventh in the league table and were knocked out by FC Midtjylland in the European play-off final by losing 0–3.

[36][37] He made his debut for Brøndby on 13 July in the UEFA Europa League play-off round first leg home against VPS of Finland, a 2–0 win.

[42] Fisker made his comeback for Brøndby on 11 July 2019, coming on as a substitute in the first leg of their UEFA Europa League qualification round against Finnish club Inter Turku in which he scored off a deflection in a 4–1 win.

[44] The injury resulted in him being ruled out for an extended period of time which cast a doubt on whether he would be offered a contract extension, as it was set to expire in June 2020.

[46] Due to the temporary suspension of the 2019–20 Superliga season as a result of the COVID-19 pandemic in Denmark, chances of him making a comeback increased and finally, on 26 May 2020, Fisker made his return in a friendly against Hvidovre IF.

[47] On 10 July, he made his official comeback in the Superliga to a standing ovation from Brøndby's fans in a 4–0 home win over FC Nordsjælland.

[48] On 21 July, Brøndby's director of football Carsten V. Jensen revealed that Fisker would be leaving the club at the end of the Superliga campaign.

Despite not being particularly tall, he is a physically strong, consistent, aggressive, and hard-tackling midfielder, with an extremely high work rate,[55] which eventually caught the eye of German manager Alexander Zorniger at Brøndby IF.