A New Zealand woman says a night of group sex involving former rugby league star Matthew Johns when she was 19 has led to significant trauma.

Mr Johns has admitted he and some other Cronulla Sharks players had sex with the woman at a Christchurch hotel while on a pre-season tour in 2002, but he insists it was consensual.

Police investigated the incident but no charges were laid.

The woman will speak extensively about the incident for the first time to this Monday's Four Corners program.

"I only remember one player definitely, it was Matthew Johns. He laughed and he joked and was very loud and boisterous," she told the program.

The former international has confirmed to Four Corners he did take part in the incident.

At the time, the woman made a complaint to police.

The players told police a group of them participated in sex with the teenager and that it was consensual.

She has told Four Corners the incident was degrading.

"Every time I looked up there would be more and more people in the room and there's lots of guys in the room watching - maybe two or three were on the bed that were doing stuff to me," she said.

She goes on to talk about the impact it has had on her life.

It is understood the woman has had significant emotional trauma.

Channel Nine has taken the unusual step of naming Matthew Johns as the former high profile player involved, ahead of next week's Four Corners program.

In a statement to Channel Nine, Mr Johns said:

"It happened seven years ago. It caused great pain to my wife and family. It took us a lot to get through it and it pains me that they will have to go through it again."

Rugby league has already been dogged this season by allegations of misbehaviour, including drunkenness and allegations of sexual assault.