His teammates will have to secure qualification without him but injured Socceroo Harry Souttar is being backed to play for Australia at next year's World Cup.
The Scottish-born central defender is beginning a lengthy rehabilitation after rupturing his ACL late in last week's goalless draw with Saudi Arabia in Sydney.
The devastating news means Souttar's English Championship campaign with Stoke City is over just as multiple Premier League clubs including Aston Villa, Tottenham and Everton had been linked to the 23-year-old.
Arnold confirmed in his pre-match press conference before Tuesday's (Weds 0200 AEDT) qualifier against China in Sharjah that Souttar was looking at between nine-to-12 months of recovery.
That would give Souttar limited chance to prove his fitness before next year's World Cup if Australia do qualify, with the tournament scheduled to kick off at the end of November 2022.
Not that the Socceroos coach has any doubt the towering defender will be part of his squad in Qatar after becoming a key presence in Arnold's plans since his debut in October 2019.
"He was more upbeat than nearly anyone else in the whole dressing room after the game," Arnold said.
"That's the type of character and kid he is.
"It's a setback, he understands that, but he knows that it's going to make him stronger in the long-run and make him mentally tougher.
"As I said to him, 'you will be at the World Cup with us - get yourself ready and get yourself fit'."
