With the AFL's pre-season competition to start on Friday, clubs have begun to look ahead to rounds two and three where the number of bench rotations will be limited to 20 a quarter and the interchange reverts to the standard 3-and-1 system.

The rule changes are part of a trial to see if capped rotations should be introduced into the regular season as early as 2014, with the AFL Commission having agreed to the rule change in principle but wanting further analysis and data collection.

However, some clubs are concerned that there could be a price to pay for the experiment as they try to manage the workloads of players in the build-up to the opening rounds of the home-and-away season.

Clubs contacted by Fairfax Media on Wednesday were still in the process of bedding down exactly how they would adapt to the system, but already potential issues have surfaced.

Carlton football manager Andrew McKay detailed the challenges raised by every club contacted, pointing out how the new rules would lead to less flexibility in the selection and managing of players, which clubs value highly in the NAB Cup. ''It's a difficult time to do it [the trial] because we are trying to balance how much game time players need or should get at this time of year,'' he said.

''This certainly makes it a bit more rigid than what we would like - not having that flexibility to play guys for just 50 or 60 per cent game time,'' he said.

It is a widely held view that the restricted rotations will impact on players who play mostly forward or in defence.

''More than likely most of the rotations will be left for the midfielders, I would think, so you can keep swapping them on and off,'' Geelong football manager Neil Balme said.

''Typically, the way our unrestricted interchange system works is that it is run by the players, in a sense.

''But obviously that won't be able to happen now because they won't be able to keep count.''

Carlton is one of two clubs contacted to have already made the decision to have one person in their coach's box to deal solely with counting and monitoring rotations.

Collingwood coach Nathan Buckley has also raised the problem of bringing back players from injury in the latter rounds of the NAB Cup, a worry McKay and football departments at other clubs have run into.

''It's hard to introduce someone back from injury who hasn't played any of the internal trials or the first round of the NAB Cup,'' McKay said.

''You don't want to bring him in and ask him to play 85 or 90 per cent game time, which they will have to under these rules,'' he said.

''Or if you put him in as the substitution and someone gets injured early, then he is going to play a lot more game time than you would have hoped.''

Under the new rules, in the second and third rounds as well as the grand final, changes at quarter-time, half-time and three-quarter-time will not be included in the total cap of 80.

Interchanges remaining in the cap of 20 from the previous quarter will not roll-over into the next quarter.

Clubs will be able to have six players on the interchange and rotations will be unlimited in the first round of triple-header NAB Cup matches.

Several clubs said they would have preferred be allowed to use the total amount of 80 rotations whenever they chose, rather than being restricted to 20 a quarter.

''That way you wouldn't have to worry about getting an injury, and how that might affect your cap, for at least the first three quarters,'' one football manager said.

AFL umpires boss Jeff Gieschen confirmed there would be provisions for clubs in cases where there was a serious injury or blood rule but that team had already exhausted its 20 interchange rotations.

''In that situation, that team will be able to make an interchange to get the injured player off and get a new one on, that's just common sense,'' he said