Sydney coach Paul Roos fears the AFL's move to free agency could mean a select group of elite players' salaries swelling at the expense of their teammates.

Roos, who has spent time living in the United States, says the AFL could soon face the same problem that has dogged American sporting leagues which have both a salary cap and free agency.

"I've spoken to people in America who have mixed responses as to whether it's worked or hasn't worked," Roos told AAP.

"One of the problems in a general sense is a lot of the money's gone to the better players.

"Having spent some time with the San Jose Sharks' (National Hockey League) team owner, he said about six or seven of their players take up about 50 per cent of their salary cap.

"There's certainly going to be players that benefit from it and there's certainly going to be players that miss out because of it."

The AFL has moved to offset concerns about the upper tier of players being the main beneficiaries by restricting the form of free agency available to each club's top 25 per cent of earners.

But Roos said the fact some form of free agency would be open to any eight-year player at a club was likely to inflate their salaries compared to more junior teammates.

"That certainly has the potential to happen, that's what happened in America, that the better players got the bulk of the salary cap, so it will be interesting to see whether that happens or not," he said.

Roos questioned whether free agency was needed at all.

"There's only been one player from my memory that wanted to change clubs and that was Nick Stevens, that didn't go to the club of his choice," he said.

"Luke Ball got to Collingwood, Darren Jolly got to Collingwood, (Brendan) Fevola ended up with Brisbane, (Chris Judd) ended up going to Carlton.

"I don't think the system's been broken, but clearly it's something the players' association has been pushing for and obviously they've come to a compromise."

Geelong chief executive Brian Cook said the reigning premiers, already facing major salary cap pressures to hold together a talent-stacked list, would find it even harder under free agency.

If the new system - due to come into effect in the 2012 post-season - was in place this year, the Cats would have 14 players on their list who meet the eight-year criteria for free agency.

But Cook said with Geelong already attempting to hold on to stars being targeted by the Gold Coast, they were accustomed to trying to make sure that financial rewards were not the prime reason players would stay with them.

"You have to be really determined now to recruit players who have the right character, who are inspired by internal reward rather than money and external reward," he said.

"You have to make sure the environment is first-class and the players enjoy it and they're managed properly and treated properly and then you have a chance of keeping your list together.

"The freeing up of player movement will mean that clubs will just have to do things better, that's the major message."

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