Tradition rules as players not keen to tinker with Tests
Player resistance looms as a major hurdle for cricket administrators to clear if the push for four-day Tests is to gather serious momentum.
Australia host Afghanistan in a one-off Test next summer and there is a possibility that clash will be a four-day match.
The International Cricket Council agreed to let boards schedule four-day Tests in 2017 on a trial basis.
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The governing body is expected to discuss the matter further in 2020, including the prospect of mandatory four-day Tests, as part of a broader review of a schedule squeeze.
Cricket Australia chief executive Kevin Roberts suggested last week that four-day Tests were an innovation worth considering, adding that "perhaps it is more likely than not in the mid-term future".
England chimed in overnight by saying they will be "cautiously" back the proposal.
"We believe it could provide a sustainable solution to the complex scheduling needs and player workloads we face as a global sport," an England and Wales Cricket Board (ECB) spokesperson told London's Daily Telegraph newspaper.
"We're definite proponents of the four-day test concept, but cautiously so, as we understand it's an emotive topic for players, fans and others who have concerns about challenging the heritage of Test cricket."
However, Tim Paine has declared he would prefer Tests remain a five-day contest. Australia vice-captain Travis Head and New Zealand paceman Neil Wagner have also made it clear they are four-day sceptics.
"Five days are the ultimate Tests," Head said.
"We have gone through a rare period where we have been able to win Tests in four days. But it's quite rare.
"We may not have seen the results we saw in England (during the 2019 Ashes) without the extra day. It plays a lot with the wicket and brings spin into play, so I would like to see it stay as five days."
Wagner, ranked second on the International Cricket Council's Test bowler ranks, said he was a firm believer in five-day Tests.
"There's always weather and other stuff around, you can lose a day," Wagner said.
"The first two Tests (in the current trans-Tasman series) have finished in four days.
"But if you look at the Test matches that have gone five days and into a last session, they're some of the most exciting Tests in history - and there's been quite a few in the last year or so."
South Africa skipper Faf du Plessis, whose side hosted Zimbabwe in a four-day Test in 2017, has previously advocated for Tests to remain five days.
There was initially much resistance from players regarding day-night Tests, the most recent major change to the longest format, but the pink ball has now been embraced by most boards.