He is the son of former Esbjerg top scorer Henrik "Ismand" Nielsen.

[3] A few months later, he went on a trial with English Premier League club Manchester City.

[4] His contract was prolonged in January 2013, where he officially was moved up into the Esbjerg first team squad.

[9] On 17 July 2022, Club Brugge announced that they had reached an agreement to transfer Nielsen from Union SG.

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