City confirmed that former Athletic captain Susaeta mutually agreed to terminate his contract with immediate effect due to family reasons.
Susaeta, who joined City from Japanese giant Gamba Osaka in January on a six-month deal, has returned to Spain after not joining his team-mates in New South Wales quarantine ahead of the season restart.
The 32 year-old winger scored two goals and set up another for City – part of the City Football Group (CFG) – in 10 appearances before the league was suspended in March due to the COVID-19 pandemic.
"The club would like to thank Markel for his contribution over the past season and wishes him well for the future," City said in a statement.
City was second in the table after 23 matches prior to the coronavirus crisis, eight points behind leader and defending champion Sydney FC.