 However, Frederiksen would have to lead the Denmark under-21 team through the 2019 UEFA European Under-21 Championship before starting in his new position.In Brøndby, he had a mixed start and the club suffered a string of poor results in September.This saw him change the formation from a 4–3–3 to a 3–5–2 in early October, which resulted in a derby win over FC Copenhagen.