Essendon coach James Hird says tactically it would "make sense" if the AFL's new substitute rule forced midfielders to spend more time up forward this season.

All clubs will field three interchange players and one substitute this season, with the sub able to be used at any time and the player he replaces not eligible to return to the field.

Hird said that Richmond coach Damien Hardwick was probably right on the money when he suggested last week that star midfielders were likely to play more minutes in 2011.

"He's a smart man. He (Hardwick) is probably right," Hird said on Wednesday.

"More midfielders would spend some time up forward, that would make sense, just because there's one player less to rotate through (midfield)."

Hardwick, a former Bombers team-mate of Hird's, also feels the second-ruckman position could come under threat but clubs will just have to see how things develop during next month's pre-season NAB Cup.

"It won't change my coaching style because I haven't coached before," said Hird, flashing a boyish grin.

"It will be different. There will be less rotations.

"Certainly the game will change a little bit because of it but who knows how it will change?

"We're trying to think through that at the present."

Hird sounded a warning to back-up ruckmen, saying they needed to be versatile with only three interchange players allowed on the bench.

"It depends who they are. If they can play forward they're definitely not (under threat), if they can play back they're not," he said.

"But if all they can do is ruck maybe they're in a bit of trouble."

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