Western Bulldogs coach Rodney Eade warns the AFL's new interchange rules could have the opposite of their intended effect and increase the pressure on clubs to field injured players.

The AFL has cut the number of interchange players from four to three, backed by an additional soccer-style substitute, with the player they replace barred from returning to the field.

As well as stemming what has been an accelerating rate of player rotations in recent seasons, the changes are aimed at limiting the disadvantage for clubs who have a player injured mid-match.

But while Eade said rotations probably would decline, he predicted the disadvantage caused by injuries would be exacerbated and the new system would become a magnet for controversy.

"It will be interesting to see how injuries affect games now, affect the result," Eade told AAP.

"They say they're doing it partly for injury-rate decline and fairness.

"But if you get a couple of injuries it's going to have a bigger bearing with three against two (fit available interchange players), rather than four against three, as in the past."

Eade said clubs would have to weigh up whether to hold their substitute back in case of injury, when deploying them earlier might provide a game-winning strategic advantage.

"The trick will be if you make a tactical move at whatever stage that is and then you get an injury and you're short," he said.

"Then it will be an interesting one for the AFL, do you put that injured player back on because you're going to be one short?

"Then there's an occupational health issue. Who's liable for that if you put an injured player back on? It could cost you a game (if you don't).

"So I can see there'll be a whole range of interesting questions asked."

Meanwhile, Eade said he would like to see NAB Cup matches gradually lengthened throughout the competition, so that by the grand final they equalled home and away games.

Currently, NAB Cup matches other than the opening round triple-headers are 17.5 minutes per quarter, plus time-on, compared to 20 minutes in the regular season.

Eade, who guided the Dogs to last year's pre-season premiership, said that meant a downside to staying in the knockout competition, as the eliminated sides went on to play practice matches of regular-season length.

"If you play all four (NAB Cup rounds), you're playing all four games that are 20 minutes less than a normal home and away game," he said.

Eade said winning the pre-season competition last season was good for the club, because it gave the `Dogs a long-awaited piece of silverware, but had no notable positive or negative effect on their premiership season.

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