Rugby league star Benji Marshall is being investigated by police after an alleged assault in the early hours of Saturday morning.

NSW police want to speak with the 26-year-old, who is believed to have been at the scene of a fight at a fast food restaurant in George Street in Sydney's CBD.

Police attached to The Rocks Local Area Command are investigating the alleged assault, which comes just days after Marshall was unveiled as the face of the 2011 NRL season.

Police released a media statement confirming an incident took place, starting with a verbal altercation between a 24-year-old man and a 26-year-old man at around 3.20am (AEDT) Saturday morning.

Marshall had earlier been hosting A Children's Cancer Institute Australia (CCIA) benefit.

The 24-year-old reportedly sustained a small facial laceration and reported the incident to The Rocks Police Station.

The event comes just three days after Marshall confidently declared he "wants to be the player that kids want to be when they grow up".

It looms as another black eye for the sport, which is currently reeling from a betting scandal plus the drink-driving charge against reigning Dally M medallist Todd Carney.

Two years ago Manly's Brett Stewart was a key figure in the NRL's marketing campaign before he caused the game's flagship television commercial to be re-edited when he was banned after an alcohol-fuelled evening and charged with sexual assault ahead of the 2009 season.

Stewart was eventually cleared of the charge.

Off-field dramas are something the previously clean-cut Marshall, who was chosen to launch the 2011 season in the NRL's heartland of western Sydney on Wednesday, had been determined to avoid.

"After the past couple of years it was sort of a curse they reckon," he told reporters at the launch on being the face of the NRL.

"It's not going to change what I do away from the game or what I do in the game.

"I want to be the player that kids want to be when they grow up.

"I've had a pretty clean image and I want to keep it that way.

"I'm pretty wary of where I am and what I do to make sure I keep the same image because I know image goes a long way in life and at the end of my career I want to still have that image."

Marshall's club Wests Tigers released a brief statement confirming the New Zealander would co-operate with police.

"Wests Tigers can confirm that they are aware of an incident involving one of their players, Benji Marshall, in the early hours of this morning," the statement read.

"Marshall has briefed the club fully on all circumstances surrounding the incident and will co-operate fully with any police enquiries that may result from this matter.

"It would be inappropriate for the club to make any further comment at this stage."

The NRL also released a statement saying they would closely monitor the affair and conduct any additional inquiries they deem necessary.

"It is always important that the club is given the opportunity to examine the facts and report to the NRL before we determine whether there is a need for intervention on our part," NRL chief executive David Gallop said in the statement.

"This will also no doubt depend on some of the issues being investigated by police.

"Clearly it is in everyone's interests to determine the matter as soon as possible."

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