Rookie NRL coach Ivan Henjak is sticking firm with his youth policy in a bid to advance an injury-hit Brisbane into Sunday week's NRL grand final.

Henjak on Tuesday announced the shock selection of 20-year-old utility Alex Glenn to replace injured halfback Peter Wallace in Saturday night's NRL preliminary final against Melbourne at Etihad Stadium.

Glenn's selection caught everyone by surprise and when he failed to train with the side - and PJ Marsh and 19-year-old Ben Hunt ran the plays - there were cynics suggesting it was all a big ruse.

Sources within the Storm camp said they were still expecting veteran Tonie Carroll or running backrower Ben Te'o to line-up at five with Darren Lockyer taking over at No.7.

But Henjak countered, saying Glenn had not trained early in the week for a few months and both he and young winger Antonio Winterstein had been excused from the session.

Immediately after naming Glenn as his No.7 choice, Henjak said the New Zealand-born youngster was off limits to the media.

That only added to cynics accusing Henjak of trying to pull a swifty on Melbourne coach Craig Bellamy.

"I don't think he needs all the extra attention," explained Henjak.

"It's a new position, he's got to get his head around it and I'd just like him to be able to concentrate on that this week."

Glenn played every game for the Broncos' under 20s side last year, leading them to the grand final.

He has played 25 of Brisbane's 26 games this season, a remarkable effort and bettered only by Winterstein and his under 20s teammate from last season, Andrew McCullough - neither of whom have missed a game in 2009.

Exciting winger Jharal Yow Yeh is another star graduated from last year's under 20s who has justified Henjak's faith in sticking with his young players.

"Those kids have done a hell of a job for us," said Henjak after revealing his hand on Tuesday before training.

Henjak had a number of options to cover for Wallace (broken ankle) including playing Carroll, PJ Marsh, Karmichael Hunt or even big Dave Taylor in the halves.

But he wanted to minimise any disruption to his team by not changing any key positions.

"We'll see how he (Glenn) goes but we're going to go with the 17 (players) that have been with us over the last two months," he said.

"The guys who have been playing in their positions have been going really well and I'm reluctant to upset their game and the confidence they've build with the players around them."

Glenn's under 20s coach Anthony Griffin applauded his selection and was confident he'd cope with the pressure.

"He's a leader, it's probably one of his strengths," said Griffith, whose young Broncos knocked minor premiers Manly out of the Toyota Cup finals 24-10 last weekend.

"He's always talking. He gets his head right in a game and not quiet at all.

"He's got a high work rate and he is used to defending on the edge."

Glenn's size will be an asset with Henjak planning to stop Melbourne up the middle.

Glenn and Lockyer are both left foot kickers which means young McCullough and Hunt will probably be called on for last-tackle options.

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