The halfback, who will turn 25 on the day he makes his first grade debut, was one of the stars of the Albion Park-Oak Flats under 18 team that took out the Group Seven premiership in 2012.

It was a team stacked with talent, with Clune and Drew Hutchison [who now plays for the Roosters] combining to dominate their opposition.

But while Hutchison received an NRL call up in 2015, Clune has been forced to bide his time in reserve grade before being named to start for the Dragons in Monday's clash with the Bulldogs.

For Sainsbury, who coached the pair at the Eagles, that wait is exactly what will help the halfback thrive at the elite level.

"With Adam, he always had to come through the way he has," Sainsbury said.

"Being smaller, people wrote him off, but he's showed that he's tough enough and his skill level is second to none.

"Adam's tenacity and attitude has helped him get to where he is now.

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"Most people would have thrown in the towel and spat the dummy, but he's always had that attitude to keep going.

"I coached him in 15s, 16s and 18s and he's always had a good head on his shoulders."

The 2019 NSW Canterbury Cup Halfback of the Year enters a St George Illawarra side under a pile of pressure, the team reeling from last week's listless loss to the Warriors.

With his job on the line, coach Paul McGregor made a number of changes to the squad, the most notable being Corey Norman's shift to fullback and Clune's inclusion. '

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While it's never ideal to enter a struggling team, Sainsbury is confident Clune has the skillset, and attitude, to take control of the Dragons' rudderless attack.

"He'd probably be one of the best halfbacks I've ever seen play - that's at any age.

"I've played with a couple of good sevens, but in all the years, he's up there with the most amount of skills.

"He can run, he can kick, he can pass, his attitude is second to none - it's been good from a young age."

Clune's selection for St George Illawarra took a concerning turn on Tuesday when the halfback suffered a suspected broken nose at training.

While he will be monitored throughout the week, the Dragons expect Clune to take the field on Monday.

"He did cop a bit of a whack on the nose and will have a bit of a follow up over the next few days," a St George Illawarra spokesman said.

"He's a tough kid though, and still very much looking forward to his debut."

At just 172 centimetres and 82 kilograms, the knock wasn't the first Clune has taken throughout his career.

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Sainsbury has watched the undersized halfback get straight back up each time he has hit the deck and has no concerns the nose will be an issue on Monday.

And with the implementation of rule changes to speed up the game, the mentor said it's those bigger bodies normally dishing out punishment who should be cautious around Clune.

"He's never had an issue with being tough enough. I'm sure he'll be out there and it won't worry him on the field," he said.

"He's lightning off the mark, so the new rules will suit him. He had a few injuries, but he's back flying again, so I'd love to see him in the clear on Monday."