On 6 September 2019, he scored his first goal for the senior squad in a Euro 2020 qualifying match against Slovakia for a 0–1 lead. Croatia won the game 0–4. On 13 October, Vlašić scored yet another opening goal in a 1–1 draw with Wales. On 16 November, he scored the equalizer against Slovakia at home, leading to Croatia's 3–1 victory and qualification for the tournament. However, in March 2020, the tournament was postponed for a year due to the COVID-19 pandemic.