[2] On 27 September 2015, Valentin got his Superliga debut in a game against AGF, who FCN won 2–0, where he came on the pitch in the 93rd minute, replacing Oliver Thychosen.

In September 2017, Valentin suffered from a horrible ligament injury in his knee, that would keep him out for at least eight weeks.

[5] In November 2018, Mads changed his shirt name from his nickname "Mini" to his middle name "Valentin" to honor his family.

[7] Valentin got his official debut on 17 August 2019 against Borussia Dortmund where he also was noted for an assist in a 5–1 defeat.

[10] Valentin was called up to the senior Denmark squad for friendly matches against the Netherlands and Serbia on 26 and 29 March 2022, respectively.