Sydney Roosters head coach Trent Robinson has branded the behaviour of Mitchell Pearce "unacceptable" after standing him down from all training commitments pending an investigation into a lewd act caught on video.

"For us, it is between us and the NRL to resolve. We will let you know when that time comes," he said.

"The behaviour was unacceptable. We understand that. We can't accept that and we won't."

The Daily Telegraph reports that Pearce could be stripped of the club's captaincy and fined up to $50,000, and is likely to be banned from travelling to the UK for next month's World Club Challenge.

In the video obtained by A Current Affair , a clearly inebriated Pearce is seen making advances towards a fellow partygoer and being reprimanded for urinating on himself and a couch at a home in Sydney late on Australia Day.

After being rejected by the woman, he can be seen turning his attentions to a Maltese terrier and simulating a lewd act on the dog as its owner tries to snatch it away.

A Roosters official told the Telegraph that Pearce, 26, would undergo counselling and have a permanent alcohol ban enforced.

"Mitchell obviously needs to be severely punished but he also needs professional help," the official was quoted as saying.

"At this stage he'll lose the captaincy, be heavily fined and we won't take him to England."

Animal welfare group the RSPCA NSW has said it was "appalled" by the video and will conduct its own investigation.

In the 90-second video, the dog's owner repeatedly pulls the pet off Pearce, before he picks it up and performs the lewd act again.

"I wanna f--- a dog, I don't even care anymore," Pearce said.

"I care. You've peed on my couch, you've peed on yourself. Get the f--- out," the party host then said.

Pearce is then seen being led out of the party with a crowd of people.

Earlier on Australia Day, Pearce uploaded an image to Instagram on his way to a Sydney Harbour boat party.

An image uploaded by Mitchell Pearce earlier on Australia Day. (Instagram/mitchpearce_7)