Brisbane Broncos' Ezra Mam 'adamant' Sydney Roosters' Spencer ...

An upset Ezra Mam has told Brisbane officials he is adamant Sydney Roosters prop Spencer Leniu racially abused him in the NRL's season-opening Las Vegas double-header.

In an incident that threatens to overshadow rugby league's march into the USA, Leniu was placed on report late in the Broncos' 20-10 loss at Allegiant Stadium.

The NRL has confirmed they are reviewing the matter, which could lead to Leniu being sent straight to the judiciary on return to Australia if charged.

Indigenous All Stars captain Latrell Mitchell also demanded the NRL take action, posting to Instagram: "I stand with you Bala. NRL better deal with this shit". Under a post about the accusation against Leniu he also wrote "Typical!".

Gee said he did not hear the alleged slur himself, and asked Mam if he wanted to make a formal complaint, to which Mam responded: "Yes I do."

When placed on report by Gee, Leniu could be heard saying to the referee: "Why would I say that?", while teammate Lindsay Collins tried to calm him down.

Leniu, who moved from Penrith to the Roosters in the off-season, told Triple M after the match that he was not "worried at all", and that the incident was "just fun and games on the field, that's it".

But Broncos coach Kevin Walters said Mam was "pretty upset" and "adamant" a racial slur had been made.

"We'll leave it with the NRL. They're looking at it," Walters said.

"We certainly support Ezra."

Spencer Leniu tried to dismiss the allegation as "fun and games" after the match.(AP: David Becker)

Broncos captain Adam Reynolds said he personally had not heard the slur, but was shocked by the allegation.

"I was well away from it. We support our player. He's pretty upset," he said.

"We certainly don't stand for racism. We'll support Ezra, get around him, make sure he's alright.

"It's never nice to hear any sort of racism, slur or anything. In this day and age you wouldn't think it's still out there. It's a bit of a shock."

Sydney Roosters coach Trent Robinson said in his press conference he had spoken to Samoan Test representative Leniu about the game, but not the allegation yet, but said it was important a process was followed.

"Ezra's adamant? That doesn't mean it's right," Robinson said when told what Walters had said.

"He obviously made the complaint, but that doesn't mean that it's right. It'll go through the formal process as it should."

The incident came in a brutal but entertaining win for the Roosters to start the season, in front of 40,746 fans at Allegiant Stadium.

AAP