Cape Town - There would be "significant player resistance" around the world if a shift to four-day Test matches was imposed, according to the Federation of International Cricketers' Associations.
The England and Wales Cricket Board has offered a "cautious welcome" to the suggested four-day model, which would see each day's play extended by eight overs in a bid to save on staging costs.
However, following England's thrilling victory over South Africa which lasted the distance in Cape Town, both all-rounder Ben Stokes and captain Joe Root threw their support behind the traditional five-day Test format.
England director of cricket Ashley Giles says Test cricket is precious to him but that the ECB are right to look at all proposals.
"If we played four-day cricket, I fear we would miss out on a lot matches like yesterday [Tuesday]," Giles told BBC Radio 5Live.
"I know a lot of Test matches now don't go to the fifth day - but you know it is precious to me, and I know it is to the players."
He added: "I think it's important we look at everything.
"There is a decision far from made yet, but it is a responsibility as the guardians for the game in this country to look after everything that would take the game forward, and also look after the workloads of our players."
Stokes claimed the last three South Africa wickets with 8.2 overs remaining at Newlands which helped deliver a 189-run victory to level the series at 1-1.
Afterwards, Stokes claimed cricket was "made for five" days.
He said: "It's called Test cricket for a reason. They should change it to 'easy cricket' if they make it four days."
The FICA is the global players' representative body in cricket and has conducted extensive research on the matter among its membership.
FICA executive chairman Tony Irish stressed there was "currently a lot of negative sentiment" concerning the suggested proposed changes.
"We continue to follow this issue closely and understand that discussions are taking place at various levels on this," Irish said in a statement on the FICA website.
"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.
"Given the obvious cricketing implications, if the ICC (International Cricket Council) and/or (national) boards do want to make a broader case for four-day Test cricket, we would need to clearly understand what both the economic and scheduling benefits would be, so we can discuss that with players and gauge genuine collective feedback.
"It is particularly important for us, and the players, to understand how any additional calendar space in the playing schedule would be used.
"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 added: "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."