Casper Nielsen

Esbjerg

Nielsen signed his first professional contract with Esbjerg in June 2009 only 15 years old. A few months later, he went on a trial with English Premier League club Manchester City. His contract was prolonged in January 2013, where he officially was moved up into the Esbjerg first team squad. Later in the season, he made his professional debut on 12 May 2013 in a 2–0 win against Copenhagen.

Odense

In January 2017, Nielsen signed with Danish Superliga team Odense BK on a 3+1⁄2-year contract.

Union SG

On 4 July 2019, Nielsen joined Belgian club Union SG.

Club Brugge

On 17 July 2022, Club Brugge announced that they had reached an agreement to transfer Nielsen from Union SG. Nielsen signed a four-year contract to keep him with Club through 2026. He scored his first goal for Club on 14 August 2022, the winner in a 3–0 victory over OH Leuven.

Standard Liège

On 2 July 2025, Nielsen signed a three-year contract with Standard Liège.

He was called up to the senior Denmark squad for friendly matches against the Netherlands and Serbia on 26 and 29 March 2022, respectively.

As of match played 4 May 2025

Club Brugge

Belgian Pro League: 2023–24 Belgian Cup: 2024–25