Football Federation Australia are undergoing their own injury assessment on Mooy, who suffered an MCL tear earlier this month against Arsenal, with an update from the FFA expected on December 24.
The Socceroos will then have until six hours before their first group game against Jordan to name a replacement for the midfielder should he still be deemed unfit to play.
While Mooy's club believe he will be sidelined, Arnold and the player himself are hopeful he can still take part.
"The most important thing around this is Aaron. He wants to go to the Asian Cup, he asked for the second opinion," Arnold said.
"He believes that he will be ready and so do we. It's one step at a time and there's a process we have to go through and we'll do that.
"I expect Aaron to be there. It's a long tournament."
While Arnold is optimistic about Mooy, he revealed he's told a dozen players to be ready for call-ups should injury strike.
"We've got probably 12 standby players, but I don't want to publicise the standby players because that seems to become the headline more than the 23 selected," he said.
"The players know they're on standby."