Bager is a product of Randers FC's youth academy. In winter 2015 Bager went on a training camp with the first team squad to Spain.[2]
He made his first team debut on 9 July 2015 against Andorran club UE Sant Julià in the UEFA Europa League qualifiers; Randers won 3–0.[3] He came on the pitch in the 76th minute, where he replaced Johnny Thomsen. Later in the same season, Bager also made his debut in the Danish Superliga against FC Nordsjælland on 28 November 2015.[4]
He was officially promoted to the first team in October 2015.[5] Bager's contract was extended in September 2016 until 2020.[6]
Union SG
In May 2019, Bager signed a three-year contract with Belgian First Division B club Union Saint-Gilloise.[7][8] He made his debut for the club on 10 August as a substitute in stoppage time for Teddy Teuma in a 1–0 away win over Virton.[9] During his first season at the club, he was mostly a substitute, making 8 total appearances.[1]
In his second season Bager played more, and he scored his first goal for the club on 25 October 2020 in a 6–0 win over Club NXT.[10][11] As he finished the season with 22 appearances, in which he scored 2 goals – both against Club NXT – Union Saint-Gilloise managed to win promotion to the Belgian First Division A as champions.[12]
Bager joined Sporting Charleroi on 13 July 2022, signing a two-year contract with an option for an additional two years.[14] He made his competitive debut for the club on 23 July, the first matchday of the season, coming on as a substitute in the 87th minute for Stefan Knezevic in a 3–1 home win.[15] On 11 February 2023, he scored his first goal for Charleroi, heading home a Damien Marcq corner-kick in a 3–0 league victory against Seraing.[16] He suffered a calf injury in late February 2023, which kept him sidelined for a month, and he returned to practice on 28 March 2023.[17]
IFK Göteborg
Bager joined Swedish club IFK Göteborg on 16 July 2024, signing a three-and-a-half-year contract.[18]
International career
He has represented Denmark at youth international level from under-16 to under-21.[19]
^"Jonas Bager est Zèbre !". RCSC – Sporting de Charleroi (in French). 13 July 2022. Archived from the original on 19 July 2022. Retrieved 18 October 2022.