[2] On 19 December 2017, Frøkjær-Jensen signed a three-year professional contract active from the summer 2018, which also meant, that he would be promoted permanently to the first team squad.
He started on the bench, before replacing Nicklas Helenius in the 73rd minute in a 4–0 victory against Akademisk Boldklub.
[4] Frøkjær-Jensen made his Danish Superliga debut on 14 April 2019 against FC Midtjylland coming in from the bench with 17 minutes left.
On 24 January 2020, OB confirmed that Frøkjær-Jensen had signed a contract extension until the summer 2024.
[6] On 11 July 2023, Frøkjær-Jensen signed for English Championship club Preston North End for an undisclosed fee on a four-year deal.