Teenage NRL debutant Robert Lui is anything but a fill-in - he's the man Wests Tigers officials have earmarked to partner Benji Marshall for years to come.

Lui will make his NRL debut against Cronulla on Sunday, the Townsville junior getting a crack at the Tigers No.7 jumper courtesy of a broken leg to Shannon Gallant.

But the 19-year-old is no stop-gap measure, given stop-gap measures don't normally get tied to four-year contracts while still in their teens.

No, Lui is seen as the real deal, and he has four weeks to prove he's the answer to a problem that had vexed the Tigers since Scott Prince upped stumps and headed for the Gold Coast.

"I don't want too much pressure on the kid, but he's got a lot of class," assistant coach Royce Simmons said.

"I don't think he'll play too much lower grade football after this week. That's a pretty big wrap to give a player.

"He's a very mature young bloke who will take the field with a lot of confidence and won't be too scared to tell the forwards where to go and won't be too scared to demand the ball."

Asked if the spot was his to lose, Simmons said: "There's only four rounds left in the competition and you're in the starting line-up.

"I think you're in a good position to be in the starting line-up next year."

Brought to Sydney as a 15-year-old, Lui has impressed the Tigers with every step of his development, so much so that they've already got him tied up until the end of the 2011 season, with an option for 2012 in the club's favour.

Coach Tim Sheens brought him into train with the top squad a month ago with a view to having him on standby for an injury in the halves.

But so impressive have his performances been since then that Sheens has opted to move Tim Moltzen - who has been the halfback during the Tigers' current five-match winning streak - to fullback to replace Gallant, with Lui coming in at the scrumbase.

"He's played well all year in the under-20s," Simmons said.

"But particularly the last month since we've rewarded him by bringing him into training, his attitude has been very good and he's played very good in that time."

Worried about upsetting the chemistry four weeks out from the finals and with the side finally having cracked the top eight, Sheens consulted his senior players before bringing Lui into the team.

He need not have worried.

"Coach asked us if we had the confidence in bringing Robbie up into first grade and we were 100 per cent behind that," skipper Robbie Farah said.

"He deserves his opportunity, he's got the backing of us boys in first grade.

"We're just looking forward to playing with him now and hopefully he can take the way he's been playing in 20s and bring it into the top grade.

"He's an impressive kid, you see him in the 20s and you know that he's a class above that level."

Brought to you by AAP © 2024 AAP