[3][4][5] A pure product of the Lorient Academy [fr],[6][7] Junior Kroupi started playing with the National 2 reserve team in the end of the 2021–22 season.

[13][14] Eli Junior Kroupi made his professional debut for FC Lorient on the 3 June 2023 during a home Ligue 1 against Strasbourg, to be the youngest player in his club's history breaking previous record of Mattéo Guendouzi,[15] when he replaced Romain Faivre at the 83rd minute and his team won the match 2–1.

[16][17] Despite this being the last round of the 2022–23 French top flight, Kroupi became at the age of 16 years and 345 days, the third youngest player to enter the field that season, only behind Warren Zaïre-Emery and Leny Yoro.

[18] On 23 September 2023, he scored his first Ligue 1 goal for Lorient in a 5–3 away defeat against Nantes,[19] to be the youngest scorer in club's history, breaking previous record of André Ayew.

[22] On 3 February 2025, Premier League club AFC Bournemouth agreed to sign him for an undisclosed fee, he is set to remain at FC Lorient until the end of the 2024–25 season.