NRL CEO Todd Greenberg said today the NRL will continue to work with police to prevent crime figures infiltrating the game.
He said police had warned Sharks player Andrew Fifita against associating with a known criminal.
Mr Greenberg said the Integrity Unit will make further inquiries into that matter - including suggestions that the player was using messages on his arm band to support a convicted criminal.
"Clearly it is inappropriate to use any club clothing or accessories to support someone with a criminal conviction," Mr Greenberg said.
"Players are generally free to support any person or cause they like. But in circumstances such as these, they cannot use our game as a platform to do that.
"We understand players have a life outside their club and the game and that may include mixing with people who have gone down the wrong path in life.
"But players must ensure they do not engage in any activity which damages our game."
Mr Greenberg said the NRL was reluctant to introduce new laws relating to messages on arm guards or other apparel.
"This is a matter for common sense and we would hope the clubs and players can do the right thing without the need for new rules," he said.
"Arm guards can often be used for messages of support for family, sick children and other worthy causes and we would prefer not to get in the way of that."