Twenty-five-year-old Gallagher is a Chelsea academy product, having moved to Atletico Madrid in August 2024. He played a total of 77 matches for the Spanish club, scoring seven goals and providing an equal number of assists. This season, however, he primarily featured for "Los Colchoneros" from the bench, prompting him to seek a new club during the winter transfer window. Aston Villa also showed interest, as reported by AFP.