Sydney coach Paul Roos says it's time the AFL had a serious look at introducing a substitute system to help cope with injuries during matches.

"One thing today, with the amount of money, the jobs on the line whether it be coaches or players or whatever, it's probably time we need to explore it," Roos said on Wednesday at the SCG.

" ... If you lose two (players early) it's almost impossible to win.

"I don't think anyone wants to see games decided by players injured. It's just unfair.

"It does happen a fair bit so I think it is time to open that debate, with the amount of money involved in footy."

Three members of the AFL's eight-man laws committee, Fremantle skipper Matthew Pavlich, Richmond great Kevin Bartlett and players' association chief Brendon Gale, have backed calls for an injury substitute rule.

The substitutes rule was trialled by the league during this year's pre-season competition.

The issue has become topical following North Melbourne's woes when they were left a player short on the field late in Saturday's loss to St Kilda.

The Kangaroos led early but fell away under the weight of their injury toll, eventually going down by 46 points.

Coach Dean Laidley cited the match as a "prime example" of the case for clubs to be allowed injury substitutes in addition to the existing four interchange players.

"If you're a coach and you lost two players in the first half like Dean (Laidley) did," Roos said

" ... I think he would probably acknowledge St Kilda were just too good but there have been games that were won and lost on injury and I don't think we should see that."

Brisbane coach Michael Voss has joined Collingwood's Mick Malthouse and Fremantle mentor Mark Harvey in calling for a new rule on substitutes.

If there was a widespread push for a new rule then the league would investigate the idea, AFL football operations manager Adrian Anderson said on Tuesday.

In the pre-season trial, clubs were allowed two designated substitutes as well as six interchange players.

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