Liga de las Naciones de la UEFA
On 6 September 2018, an understrength Ireland lost 4–1 to Wales in their opening game in the UEFA Nations League. Ireland went on to finish bottom of their group, picking up just two points in two 0–0 draws against Denmark and were relegated to UEFA Nations League C for the 2020–21 UEFA Nations League. On 21 November 2018, O'Neill parted company with the FAI.