MELBOURNE coach Dean Bailey has concerns about how free agency would work if introduced in the AFL.

Bailey said a number of issues had to be worked through before he would back any form of free agency as mooted by the AFL Players Association.

"I think that's going to take a fair bit of debate about what age and how long service and [how many] games [a player has played before free agency is decided]?" he said on the first day of Melbourne's pre-season training at Junction Oval.

"If you start footy at 21, is the age 27? [Then] he's only there for six years.

"I think there is a lot more to it than thinking: 'Gee, it's a great thing for this situation to work for free agency'. There is a lot more to it."

Working on the hypothetical scenario of an eight-year player moving on to a rival AFL club under free agency, Bailey highlighted several divisive points.

"His first year or two … for a start, he's on a fixed contract with the AFL, so it's the next four or five years when you get a player to an age of 24 of 25 – and hopefully he's got 100 games under his belt – he's just about to repay the club by having his best years of football," he said.

"You could argue at the age – is he good enough to stay at the club? Yes he is, because he's about to play three of four years, 60 games, at his premium."

Although Luke Ball was unable to secure a new club during last week's trade week, Bailey said the former St Kilda captain still had several options in front of him, including Melbourne.

"In Luke's situation, they (St Kilda) couldn't get a deal done, but in some ways he's got an opportunity to go in the national draft or come through the pre-season, so his options are still open," Bailey said.

Bailey said the fact 23 players shifted clubs last week – as opposed to six in 2008 – showed the football industry that the exchange period could work.

"This year there were more trades than ever, so I think people have been concerned that there wasn't enough movement amongst clubs," he said.

"I'm sure the AFL found the week exciting and I think most of the media at least had some interest, rather than the last morning of trade week, which is normally the rush around when you're trying to get one or two done."