AFL chief executive Andrew Demetriou has confirmed he sent a memo to all AFL clubs reminding them of the importance of pre-season competition, after a string of blistering attacks on the NAB Cup.

Since pre-season began on February 24, the AFL has been forced to weather continued criticism from coaches and observers about scheduling and rule changes, with St Kilda coach Grant Thomas the most outspoken.

Last weekend, Thomas said the NAB Cup was a waste of time and diluted the AFL brand, adding the scheduling of matches in late-summer heat could have safety implications for players.

Rule changes led Collingwood coach Mick Malthouse to jibe that players should start wearing netball bibs, while former AFL chief executive Wayne Jackson said the game was becoming soft.

In Perth, Demetriou confirmed he had sent a memo to all clubs reminding them of the "importance of the pre-season competition" and the AFL's heat policy.

But Demetriou said he welcomed debate into the pre-season, particularly rule changes, saying discussion was welcomed and acknowledged.

"I think it is a healthy thing, the debate and discussion around the rules - we want people to have their say," Demetriou said.

"I think it has been forever been thus ... there is always debate around it.

"No, I don't (think coaches are treading a fine line) - I think it is all good, healthy banter and I encourage everyone to speak about the rules and the competition, and we take comments on board."

Thomas, Malthouse and Fremantle coach Chris Connolly were all critical on the weekend.

The Fremantle-Collingwood NAB Cup quarter-final at Subiaco and St Kilda's challenge match against West Coast in Mandurah were played in 30-plus degree heat.

But Demetriou said the competition was valuable on several levels.

"It allows all our supporters to see how their clubs are travelling, showcases new draft choices, and allows clubs to win a prize - $220,000 is not something to be sneezed at," Demetriou said.

"And it also allows to take the game around the country, to grow the game."

Meanwhile, Demetriou said the off-field dramas of West Coast were not on the agenda when he visited Perth for the first time since Ben Cousins' booze bus scandal.

The AFL boss briefly met Cousins and new captain Chris Judd, having travelled west to address players and officials at West Coast and Fremantle ahead of the season proper.

Despite again saying Cousins had been foolish when he allegedly fled from a police roadside breath test, Demetriou said the subject of the club's off-field behaviour had not been raised.

"All of us involved in football know from time to time there are always going to be these incidents, or off-field dramas as you like to call them," Demetriou said.

"West Coast is a very professional football club - they have been dealing with their issues, they keep the AFL informed fully ... and if something else was to arrive they would deal with that in the future.

"I've caught up with Ben briefly, every time we see each other we have a chat, I have caught up with Chris Judd and ... congratulated him on being captain.

"Anyone would agree that what transpired was foolish, and I guess if he had his time again he would prefer not to have done it."

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