Souttar shone during Australia's run to the knockout rounds of last year's World Cup in Qatar but has yet to play under new manager Enzo Maresca following Leicester's relegation from the Premier League at the end of last season.
Despite his current difficulties at club level, the defender remains a key member of Arnold's squad as the Socceroos continue their preparations for January's Asian Cup and is expected to start alongside debutant Cameron Burgess.
"My message to him is simple and that is this is your stage," said Arnold.
"This is your opportunity to show your coach at Leicester and ask the question why you're not playing, and show the fans how good you really are.
"He's got to use that motivation to go out there and show everyone that's watching this game who Harry Souttar is and everyone will remember him from the World Cup.
"He's been working hard at the club, at Leicester. There's absolutely zero doubt in Harry's mind where he's at and he's got a great mentality and wants to show the world what he can do."
The game is the latest in a series of high profile friendlies for the Australians, who played World Cup winners Argentina in Beijing in June and are lined up to face England at Wembley in October.
Arnold will be without Mathew Leckie after the Melbourne City forward was injured in training, ruling him out for at least six weeks.
"He won't be ready for the October training camp," said Arnold. "The most important thing is Lecks' health and Lecks is fine.
"I'm very apologietic to Melbourne City, it was a complete accident. It was never intentional in any way, it's just one of those things that happens in training."
