Sydney Roosters recruit Spencer Leniu has been placed on report for an alleged racial slur directed at Brisbane Broncos five-eighth Ezra Mam.

The incident, which occurred late in the game between the Roosters and Broncos - the second of two being played in Las Vegas to kick-off the NRL season - saw the two teams come together after an aerial challenge from a kick.

Reece Walsh had been hit off the ball just plays earlier and was left in backplay, while Kotoni Staggs was also on the ground.

Referee Adam Gee then blew for time off before calling both captains out for a conversation alongside five-eighth Mam, who made the complaint.

Gee, who was joined by the two touch judges in the middle of the field, told skippers Adam Reynolds and James Tedesco, as well as Mam, that he didn't hear the comment leading to the complaint.

"Ezra has made a formal complaint that is racial in nature against Spencer," Gee said on-field.

"I haven't heard it, but the incident goes on report and it will be dealt with after. That's where it's left."

Leniu was then told specifically of the complaint by referee Gee and was picked up by TV cameras making a bewildered expression.

Asked about the incident post-game, Leniu told Triple M Radio that there was nothing in it.

"Nah nothing, it's all just fun and games on the field and that's it. I'm not worried at all," Leniu said in Las Vegas.

News Corp reports the alleged comment made saw Leniu call Mam, who is a proud Indigenous man, a "monkey".

Kevin Walters confirmed post-game that the Broncos have lodged a formal complaint with the NRL.

“He is pretty upset,” Walters said.

“Yes, he was adamant (he was racially abused).

“We got off the field and it's in the hands of the NRL, but we support Ezra and rightly so.”

It's likely that the only way the alleged incident would be able to proceed with any penalty is if there is audio picked up by the referees microphone.

Any judiciary hearing on the alleged comment would be set for a date following the team's arrivals back in Australia, with no guarantee of any hearing being on Tuesday night as is usual practice.