FFA's independent Appeal Committee of Malcolm Holmes QC, Arthur Koumoukelis and Deborah Healey convened to hear O'Donovan's appeal.
They dismissed it and as a result O'Donovan will have to serve his entire eight match suspension, of which he has already served two games.
The Mariners appealed the severity of the ban, arguing at the time that the sanction highlighted a disparity between penalties imposed by the disciplinary committee compared with the match review panel.
"When assessed against penalties imposed for similar incidents, the penalty is manifestly excessive and reflects a clear disconnection between the A-League and other leagues (both domestically and internationally)," the club said in a statement at the time.
Wellington Phoenix defender Muscat was slapped with a two-game ban for his elbow on O'Donovan in the lead up to the headbutt.