Brisbane Broncos coach Kevin Walters has raised the alarm over how the NRL's double-header in Las Vegas will be officiated.

The field being used for the opening two games of the season is slightly smaller in both length and width, with concerns raised it will cause the game to be played differently.

South Sydney coach Jason Demetriou admitted before the Rabbitohs left Australia that they had practiced on a shorter, narrower field before departing, and that the influence on the game was obvious when watching film.

“We spent a week training on it, just to get a feel for it,” Demetriou said before leaving for the United States of America per Fox Sports.

Allegiant Stadium
   Crowd: 40,746

“Get some understanding of it, but the initial feeling was that the players didn't really feel it but when I went back and watched training it's pretty obvious the dimensions do make a difference.

“It's definitely going to be more defence orientated and the weather I think could play a part as well, the cooler conditions.

“I'm excited we get a full two weeks to prep for that and we've had a week here as well.”

Allegiant Stadium
   Crowd: 40,746

Now Walters has revealed per Wide World of Sports that they want to have a meeting with the NRL around how the games will be officiated.

"It's very new to all of us so, we just wanted a chat on things like the 10-metre (offside) rule," Walters told the publication.

"The refs usually go by the lines on the field which are 10 metres apart.

"But here they will be a little less than 10 metres… so what is offside?

"If the play-the-ball is on the 20 metre line and the defence is on the 10 metre line, are they onside?

"Because technically, they will only be nine and a bit metres apart… it could cause confusion so best to sort it out before the game."

It comes as first images of the field - which was wheeled into Allegiant Stadium today - were revealed showing a clearly smaller field of play.

The games will be played on Sunday afternoon (AEDT).