Three-time AFL premiership coach Mick Malthouse has slammed mooted changes to the finals series.

The expansion of the league to 18 teams next year has the AFL looking at expanding the top eight to nine or even 10 teams.

The league is also weighing up a five-week finals series, rather than the current four-week major round schedule.

But the Collingwood coach was adamant on Friday there should be no expansion of the finals system.

"Eight out of 16 is rewarding mediocrity, quite frankly," Malthouse said.

"It's an elite competition, it has to be played in an elite manner.

"As a non-administrator looking at (it), don't worry about the dollars, don't worry about the TV rights or anything else.

"All those things are taken into consideration when you start talking about eight or nine teams in finals, (or) five weeks of finals."

Malthouse and Collingwood had to endure a five-week finals series last year when they drew the grand final with St Kilda, forcing a replay which the Magpies won for their first flag in 20 years.

"(The) finals series is the most draining period of the year, from week one to week four if you manage to get there," Malthouse said.

He wants the top eight to remain unchanged when the competition expands to 18 teams in 2012, meaning the finals become more exclusive and are a truer reward of success through the regular season.

"We may as well throw them all in and just say `look, we'll just go through 24 weeks' ... it's got to be elite and you have to strive for that," he said.

"Final eight in an 18-team (league), it puts a line there that says `underneath there is more than 50 per cent'.

"To me, 50 per cent of clubs playing in a finals series - it might be good for your record and good for your numbers, but it doesn't make a lot of sense to me."

Malthouse has also backed the pre-season competition, with the league poised to possibly scrap the current NAB Cup format.

But the Magpies coach is less concerned about what form the pre-season will take.

Collingwood will play Essendon on Friday night in the NAB Cup final and the game is expected to fill Etihad Stadium.

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