The national team's most problematic position is still there for the taking after a string of players tried and failed to nail it down as their own since the 2015 AFC Asian Cup.
Grant himself is still in disbelief over his first senior selection to Australia's extended 30-man FIFA World Cup qualifiers squad.
But Arnold says the 26-year-old former Olyroo's impressive work rate and attacking prowess fits the mould Socceroos coach Ange Postecoglou is after.
"He's got all the attributes," he said.
"Once you get to international level it's about the four pillars: tactical, technical, physical and mental.
"And a lot of it is about athleticism, and he has that - he can run all day.
"He's quick, he's aggressive and he's improving out of sight with his decision-making and last ball.
"He could probably have nearly double figures in goals as a right fullback, that's how far he's getting forward down the pitch.
"Ange has always shown he likes fullbacks that can get forward so he fits the model, but now it's about the concentration side for 90 minutes and stepping up to a new level."
The prospect of Grant and uncapped veteran goalkeeper Danny Vukovic being handed Socceroos call-ups six months ago would have seemed left field.
But the pair have flourished at the table-topping Sky Blues this season, in an environment that's also fostered the form of several other Australian players including surprise omission Alex Wilkinson.
"We've got a couple of the boys who feel a little bit hard done by as well," Arnold said.
"They feel they've been in good form as well, but it's about them keeping improving and maybe they'll be next.
"Ange has got a strong back line. Wilko has been a standout this year for us.
"His composure, his experience, and especially in big games - you can't build players for that until they get to that age.
"Wilko is such a good guy, he's not upset at all and he shouldn't be. All they can do is keep pushing."