But the NAB Cup looks set to survive any regular season expansion, with Demetriou describing it as important to player preparation and maintaining an AFL media presence.
Gold Coast will enter the competition next year, with Greater Western Sydney to follow in 2012, and Demetriou said the AFL had set up a sub-committee to determine the length of the home and away season and the structure of the finals series.
"We're actually doing a huge body of work on 17 and 18 teams," Demetriou said on Friday from Subiaco Oval, where he was attending a Fremantle Football Club function.
"As you know there'll be a bye next year (and) we're doing work around whether it'll be a 22- or 23- or 24-round season when we go to 18 teams. They're all options that we're looking at.
"Our guys are doing a mountain of work with a sub-committee that involves clubs on what the structure of the competition will look like (so) hopefully by mid-year, probably towards August-September, we'll have a better feel."
Regarding the finals series, Demetriou said the league would look at all options. The AFL has used a top eight since 1994 and the current format has been in place since the 2000 season.
"What do the finals look like? Do we still have a final eight? That's being done at the moment," Demetriou said.
"We have a top eight with 16 teams, which is 50 per cent of the competition. When you go to 18 teams someone could run the argument, 'Why haven't we got a top nine?'
"There's no reason why we can't have a top nine. Someone sent me a proposal the other day suggesting a top 10.
"We'll look at all those things and we'd remiss in our duties if we weren't looking at and canvassing all the options."
Former Essendon captain Matthew Lloyd has called for the NAB Cup to be scrapped in favour of a longer regular season, but Demetriou said the clubs were happy with the pre-season competition and the AFL needed to maintain a media presence early in the year.
"I think Matthew's entitled to have his opinion, but every club tells us they need preparation to get these elite athletes ready for a season - they can't just throw them into round one," Demetriou said.
"I can assure you that we have many clubs that, if we didn't have a NAB Cup competition and particularly a NAB Regional Challenge, it would be to the detriment of the preparation of their players.
"Not having a NAB Cup or a NAB Regional Challenge really would provide four or five weeks of no football coverage. As other codes are elongating their seasons, we actually want football to be talked about."
Demetriou was in Perth for talks with both WA clubs as well as the WA Football Commission. He said football in the state was healthy and West Coast and Fremantle were well placed as the competition expanded.
"We're very optimistic about the Fremantle Football Club, very confident in where they're heading," he said.
"The West Coast Eagles have gone through a seismic shift in culture and it's been very, very effective.
"We've got great confidence in the football clubs over here."
