Arnold was out on the pitch catching balls for only mere minutes before walking off and down the players' tunnel.
Only the first 15 minutes of Friday's session was open for media, but Arnold's early exit - on the back of not warming up with the team during Thursday's training - has raised doubts about her fitness.
Adding further intrigue, former Perth Glory goalkeeper Morgan Aquino has been flown in as a train-on player.
"I'm not too sure to be honest," Matildas midfielder Katrina Gorry said after training when asked about Arnold's fitness.Â
"I've just been focusing on myself and on the players that are out on the pitch. The physios manage her."
When asked if Arnold reappeared at training following her early exit, Gorry replied: "I have no idea sorry."
Australia's goalkeeping stocks are becoming a worry.
Star Lyon custodian Teagan Micah was initially selected but had to withdraw due to lingering concussion issues.
If Arnold is ruled out of Sunday's match, it would leave either 21-year-old Brisbane Roar shot stopper Chloe Lincoln or 26-year-old Jada Whyman in the hot seat.
Lincoln has just three Matildas caps to her name, while Whyman is yet to make her senior international debut.
In contrast, Arnold has 61 games under he belt and became a household name during the Matildas' quarter-final win over France at the 2023 Women's World Cup when she saved a series of penalties during the shootout.
Gorry has full faith Lincoln or Whyman will be able to fill the void if called upon.
"I don't know Macka's case at all whether she'll be out on the pitch or not, but regardless of if she is or isn't, we've got some great keepers in there," Gorry said.
"Maybe someone will get an opportunity, but I'm sure they're ready for it.
"It'd be awesome. I mean, they've been playing in good leagues. They've been playing good football.
"And for us, whoever's in goals, we trust them with everything."
Gorry feels like the Matildas, who reached the semi-finals of the 2023 World Cup, are primed for the Asian Cup.
"The World Cup was massive for us," Gorry said.
"We've brought in a lot of players, got a lot of experience, and then obviously Joe (coach Joe Montemurro) to top it all off, I think we're in a really good spot.
"We've had some really up and down moments over the last couple of years, but I think that's what's kind of brought us all together, and made us want more, and I think we're really ready for it."
Meanwhile, a new Team of the Tournament award has been included for the upcoming Asian Cup, marking the first player-voted honour of its kind at a continental tournament in Asia.
The FIFPRO Asia/Oceania Team of the Tournament will be voted on exclusively by players competing at the 2026 tournament, following in the footsteps of the prestigious FIFPRO World 11 award.
At the conclusion of the Asian Cup, players from all 12 competing nations will be requested to submit their votes for the top three players in each position, with those who receive the highest number of votes comprising a final Team of the Tournament.
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