 Grimaldo's maiden appearance in the UEFA Champions League took place on 13 September 2016, when he played the entire 1–1 group stage home draw to Beşiktaş.His first goal in the competition came during the same stage but on 2 October 2018, in a 3–2 away win over AEK Athens; he repeated the feat against the latter opponent on 12 December in the return fixture, his 30-meter free kick in the 88th minute helping to a 1–0 victory.Grimaldo won his first cap for the Spain under-21 team on 5 February 2013 – before he had turned 18 – playing the second half of a 1–1 friendly draw in Belgium.