England director of cricket Ashley Giles has declared five-day Tests a "precious" part of the game, as the global players' union warned dropping a day could lead to "significant resistance".
The prospect of introducing four-day Tests will be discussed by the International Cricket Council (ICC) in the near future, and South Africa has said it would welcome the move.
Although the England and Wales Cricket Board has said it is "cautiously" backing the concept of the shortened matches, it has recognised it is an "emotive" issue.
Giles may have a greater passion for Test cricket than many of the sport's administrators, having been a Test spinner for England before moving into coaching and management.
Speaking on BBC Radio 5 Live on Wednesday, Giles said: "Anything that helps players and their workloads is good to look at, and anything that takes the game forward is good to look at. But I played Test cricket, I love Test cricket, and if we played four-day cricket I feel we would miss out on a lot of matches like yesterday."
That was a reference to England's gripping fifth-day success in bowling out South Africa in Cape Town to win the second Test on Tuesday and level their series.
"I know a lot of Test matches these days don't go to the fifth day, but it is precious to me certainly and I know it is to the players," Giles said.
"I think it's important we look at everything. But I think it's a decision far from made yet.
"It is our responsibility as guardians of game in this country to look at everything that can both take the game forward and look at the workloads of our players."
The Federation of International Cricketers' Associations (FICA) has gathered early reaction from far and wide, and issued its response to the growing debate by underlining the concerns of players.
The likes of former Australia captain Ricky Ponting and India great Sachin Tendulkar have already expressed opposition to the idea.
FICA executive chairman Tony Irish said: "From our discussions with players around the world, and our global survey data, it is clear that there is currently a lot of negative sentiment, within the global collective of players, towards such a significant change to the game's most traditional format."
That could hardly have been more blunt, with Irish's statement on FICA's website going on to stress the ICC and national boards must be open about their intentions and motivations, and how cricket might benefit.
"Making a fundamental change simply in order to provide calendar space to fill with additional or meaningless cricket is clearly not something we can support. Cricket's global structure desperately needs clarity, rather than further confusion," Irish said.
"Until such a time as we and the players are provided with the full picture and compelling reasons for change, we remain supportive of five-day Test cricket, and would expect significant player resistance if a shift to that is imposed on players by the ICC and/or boards.
"Test cricket is a cherished format of the game and it needs player support and buy in to survive. We urge those making decisions to understand that."
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