After initially being linked with a move to Perth Glory,[4] Athiu signed his first professional contract with Melbourne Victory in October 2017 on a season-long loan from Heidelberg United.
[5] Victory coach Kevin Muscat initially stated that it would be some time before Athiu would make the first team due to injury and fitness concerns.
[6] Nevertheless, Athiu made his debut for the club as a substitute in a draw with Western Sydney Wanderers on 6 November after a number of Melbourne's attacking players were unavailable for the game.
[9] Athiu was eligible to represent his nation of birth of South Sudan or his country of residence in Australia prior to making his competitive debut for South Sudan against Equatorial Guinea on 4 September 2019 in the first leg of the first round for the 2022 FIFA World Cup.
Athiu was substituted on David Majak Chan at the 54th minute and assisted in the equalizing goal of the eventual 1–1 draw.