From Wikipedia: At the age of 19, Arzani was called into Australia’s preliminary squad for the 2018 FIFA World Cup on 7 May 2018. He made his international debut for Australia as an 84th minute substitute for Mathew Leckie in a friendly match against the Czech Republic on 1 June 2018.
He was named in Bert van Marwijk’s final 23-man squad for the 2018 World Cup the following day, becoming the youngest ever Australian player in a World Cup squad as well as the youngest player overall at the 2018 World Cup.
Arzani scored his first international goal for Australia one minute after being substituted on in the next friendly match for a 2–1 win against Hungary on 9 June 2018.
He made his World Cup debut on 16 June 2018 as an 84th minute substitute against France. At the age of 19 years and 163 days he became the youngest player to ever make a World Cup appearance for Australia. Arzani was used as a substitute in all three World Cup matches against France, Denmark and Peru.