Some debt-ridden NRL players have found themselves in so deep that they owe more money in gambling repayments than their massive contracts are worth, the head of the NRL match fixing probe says.

And although Strike Force Nuralda failed to uncover any truth to match rigging allegations relating to four NRL games in 2015 and 2016, there was evidence of "insider information" being passed from players to organised crime figures.

Organised Crime Squad commander Detective Superintendent Scott Cook said no charges could be laid against any of the 13 players and organised crime figures identified as "persons of interest" during the investigation because the summary charge of insider information only had a six-month statute of limitations.

"We have got no doubt there was insider information being exchanged … about players who were playing, injuries, who was feeling good, who was feeling bad, that sort of thing. Insider information related to particular clubs," Detective Superintendent Cook said.