Ivan Cleary was "freaking out" when the injured Brian To'o busted out a backflip during an impromptu dance routine for thousands of fans in Las Vegas.

But the coach says his superstar winger will return for the Panthers' next game after his sore hamstring pulled up fine from his on-stage antics.

Punters from Australia, England, New Zealand, the US and beyond flocked to downtown Vegas for the NRL's Fan Fest on Fremont Street on Friday night (AEDT).

With music pumping, punters cheering and Cronulla players throwing footballs into the crowd, Warriors coach Andrew Webster declared "the NRL has taken over Las Vegas" with its festivities.

Amid the excitement, the two on-stage emcees challenged each team to nominate their best dancer to hype up the crowd, with the Jillaroos' Sarah Togatuki and Sharks stars Braydon Trindall and Will Kennedy particularly impressive.

At pre-season training, To'o strained his hamstring seriously enough to miss the Panthers' season opener against Cronulla at Allegiant Stadium this Sunday (AEDT).

But To'o, one of the NRL's liveliest characters, said he simply could not resist a dance.

"I had to represent the brothers so that just pretty much came out," he said on the red carpet.

Penrith are beginning life without Jarome Luai, James Fisher-Harris and Sunia Turuva in round one and To'o's injury loomed as yet another blow.

But the Samoan international said his dance moves doubled as a test for his hamstring and was confident he would be back on the field "very soon".

"(It was) a bit of a test and it looks pretty good," To'o said.

As part of the routine, To'o bent down and pretended to clutch at his injured hamstring, only to body roll back up and continue dancing.

The usually unflappable Cleary admitted to being a little rattled when he saw his metre-eating winger going all out.

"I've got to be honest, I was freaking out a bit," the coach said.

"But he seems to have pulled up okay. That's good news."

To'o is expected to face the Sydney Roosters in round two and could be joined by prop Liam Henry, who will miss miss the Vegas clash with a shoulder issue.

"By the looks of last night 'Biz' should be playing tomorrow,' Cleary quipped.

"'Biz' will definitely be back next game and hopefully Liam, not too sure about him yet."

In To'o's absence, second-rower Luke Garner joins the centres to face the Sharks and Paul Alamoti starts on the wing.

But attention is likely to be fixed more closely on the inexperienced Casey McLean, who slots onto the opposite wing to replace Wests Tigers recruit Turuva.

McLean looks set to become the youngest staple of the Panthers' starting line-up since their premiership dominance began in 2020.

Now 18, McLean was a 13-year-old schoolboy at Sydney's Newington College when that season started.

But the teenager flaunted his ability with four tries for New Zealand on Test debut against Papua New Guinea last year, and has made seven NRL appearances for Penrith already.

"He's got a big future ahead of him," To'o said of McLean.

"He pretty much showcased his skills last year. There's a reason why he's in the team. I can't wait for him."