The former Adelaide United winger was feeling battered and broken after a 1-0 elimination final loss to Central Coast Mariners in Gosford back in 2014.
But as he left the field he was accosted by a consoling Arnold, who though no longer in charge of the Mariners, then made his way over to the raw teenager and offered some sage words of advice.
“I was really down and was shocked when he came to me, pulled me aside, and told me to keep listening to my coaches, to keep learning and listening,” Mabil said.
“I’ve never forgotten that moment and it meant a lot to me.
“When he first came up to me like that I thought to myself, ‘that’s not normal’. But it just shows his character.
“He’s not like one of those people who if they win they want to rub it into your face.
“He’s a man whose always looking for improvement in himself, and of course the players around him.
“But he knows also that it’s just a game and we all have to be good people.”
If goodwill towards Arnold from the 25-man squad he has named for the international against Kuwait (on Tuesday October 16 AEDT) could be bottled, then victory would already be in the bag.
But beyond his well-honed man management methods, Arnold - according to Mabil - is working on tactical nuances which will make Australia far more dangerous in the attacking third than they were under Ange Postecoglou, or Bert van Marwijk at the 2018 FIFA World Cup.
The FC Midtjylland attacker - whose side sit joint top of Denmark’s Superliga going into Monday morning's (AEDT) visit of Vendsyssel FF - could look large in Arnold’s plans to enact those philosophies going into January’s AFC Asian Cup defence in the UAE.
Having got a taste of what Arnold is aiming at achieving from last month’s Socceroos training camp in Turkey, Mabil likes what he saw.
“He’s an amazing coach. He makes everybody feel at home and wants you to get the best out of yourself, and he knows how to get the best out of you,” he said.
“I’m excited to work with him and to listen and learn from this experience.
“The game’s evolving a lot and Graham Arnold is working on something special up front to get goals - he won’t just be relying on one person to score.
“He focuses on something to get the best out of the team in that area. A lot of it is about flexibility among the front players, and I think it’s going to take Australia to another level.”
Mabil, 23, is in his third season with FC Midtjylland, but believes his struggles during loan spells with fellow Danes Esbjerg and in Portugal at FC Pacos - both of whom were relegated - have brought valuable texture to his unfolding career.
“I couldn’t see it before but the struggles that I went through just made me stronger,” Mabil said.
“It means that I’m enjoying every moment now and I’ve been able to adapt to different situations.
“I’ve had maybe five or six coaches in the last two years or so, so I’ve had to try and take advantage of every coaches philosophy.”
Deployed as a free player in a front three for his club, Mabil has made 10 appearances in all competitions so far this season and said “everything is coming together” for him.
With two years left on his five-season deal, Mabil said: “The club believes in a lot of the young players".
“And I just have to keep working hard to repay the faith they have shown in me.”
When it comes to Australia, South Sudanese refugee Mabil sees a bigger picture than just football.
Having spent his childhood among thousands of refugees at the Kakuma refugee camp in Kenya, he resettled in Australia with his mother and siblings aged 10.
He regularly returns to the camp as part of his work for the Barefoot to Boots Foundation, a charity he founded with his brother and an Australian businessman.
“Everybody wants to represent the country and Australia has given me and my family a lot,” he said.
“The only way for me to give back is to represent Australia and give all I have for the national team.”
