Wests Tigers' injury crisis has deepened with news halfback Robert Lui will miss up to six weeks of NRL action.

Lui wasn't selected in Sunday's squad to take on the Sydney Roosters because of an ankle injury, but coach Tim Sheens revealed the damage is far more serious than first thought.

In Lui's place, 18-year-old Jacob Miller has been thrown the challenge of making his NRL debut at halfback against his former club.

Sheens has no doubt Miller is ready to take on the might of the Roosters halves, Mitchell Pearce and Todd Carney.

"If you're good enough you're old enough. And I think he's good enough," Sheens told reporters.

"I've told him he doesn't have to be the best player on the field ... I'm sure he'll handle it without any problem."

The Tigers have been forced to make major changes with big names Chris Lawrence (hip), Lote Tuqiri (broken arm) and Gareth Ellis (ankle) among eight regular first grade players sidelined with injury.

"It's not ideal but the opportunity is there now for the younger ones," Sheens said.

The Tigers coach is hopeful that forward Bryce Gibbs will return from a knee injury this week, although he hasn't been named in the Tigers squad.

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