Bulldogs sensation Ben Barba is bracing himself for a mountain of defensive work in his long-awaited NRL debut against St George Illawarra at ANZ Stadium tomorrow night because he will be the "smallest bloke on the field".

Barba was called up to the bench after Ben Roberts and Lee Te Maari were stood down and fined for a nightclub altercation at Cronulla.

There are no concerns about the 19-year-old's attacking prowess. A record 27 tries in the Toyota Cup this year is testament to that. However, his defensive record isn't as impressive and the Dragons will run plenty of traffic at the halfback, who stands 175cm and weighs 85kg.

Barba said he was up to the challenge and was aiming to remain in first grade for the rest of the season.

"They'll come at me not so much because of my defence, but because I'll be the smallest bloke out there," he said. "I'm going to give it my all. This could be my first and last shot.

"Hopefully I'll get through it.

"Everyone plays to get a regular spot in first grade. That's what I want to do."

Barba said he was "over the moon" to finally crack the NRL and had to ring back twice to make sure news of his elevation wasn't a joke.