Collingwood ruckman Darren Jolly has been the most vocal opponent of the initiative, claiming it is ''bloody stupid''.

But AFL operations manager Adrian Anderson said the league was only doing what players demanded - using the pre-season competition to trial rules that could be implemented into the season proper.

''The strong feedback last year, where we introduced the substitute on the bench, the feedback was largely very positive from the clubs … but the one thing that came out strongly was if you are thinking about anything like that in the future, please trial it in the NAB Cup,'' Anderson said.

''So, we are thinking about it, we haven't made any decisions yet, but we are following the input we received last year that if we are considering something like that, we should trial it.

''There has been some of the usual ill-informed hysteria, but we'll gather all the data and evaluate the trial as we do with all of the NAB Cup rules.''

The AFL last year controversially revamped the interchange bench in the season proper, cutting the number of players from four to three and introducing a substitute.

Players were so angry they considered a ''sit down'' protest on match day.

The NAB Cup this season has two players on the bench and two substitutes, with the possibility this system could be introduced in the home-and-away season next year.

The AFL Players Association is opposed to having two substitutes. Sydney coach John Longmire and veteran midfielder Jude Bolton also expressed their concerns at the weekend.

AFLPA general manager, player relations, Ian Prendergast said players were still adjusting to logging increased minutes under last year's new ruling and it was too early to tamper with this.

''We need to look at how that works over an extended period of time so that we can monitor it effectively and see what affect it has on the game. It would be premature at this stage to consider making any further changes along those lines,'' he said.

''There are some strong views out there among players. The feedback from the players was that they felt they were more fatigued than they were previously.

''There were some general concerns in that regard. That's why we have said have a look at it over an extended period of time, not only access data on how the game is being played, but also data and evidence on the affect it is having on players, on their general wellbeing and the duration of their careers.''

Anderson said the ''three and one'' system was a success last year.

''We saw fantastic footy. We saw some of the stars of the game shine brighter, and spending more time out on the ground,'' he said. ''We saw great footy, a fairer contest, because teams we know for a fact were less disadvantaged when they lost a player to injury early in the game, and the evidence we have got to date indicates it also had an effect in moderating the speed of players, and we're advised that should have an impact on injury trends.

''We won't forget people predicted it was the end of ruckmen, the end of tall players and small players. There were all sorts of prognostications about what effect it would have.''

The new-look NAB Cup is no longer knockout, meaning clubs are guaranteed two 40-minute clashes against two opponents and two four-quarter games, with the top two teams progressing into the grand final.

The AFLPA says players want only three full matches to prepare for the season.

''The players' objective in that area is to reduce the pre-season competition and reintroduce the two byes [in the season proper],'' Prendergast said. ''They think there is real value having those two weeks rest through the season. Those two byes should be divided into the split rounds, one a third of the way through the season and one two-thirds through the year.

''We think the format that the AFL is running with this year would make it easier for us to reduce the length of the pre-season competition for the following year due to the way they decided who plays off in the grand final. It's not a knockout competition, it allows us to reduce the length of the pre-season.''