Any changes to Test cricket must be in line with in with the sport's new global structure, the head of the International Cricket Players' Union (FICA) Tony Irish said.
The International Cricket Council will meet in Auckland this week, where announcements on separate league structures for Tests and 50-over cricket are expected to be made.
Irish, the chief executive of the Federation of International Cricketers' Associations, urged stakeholders of the game not to look at ad hoc solutions to Test cricket.
"Any proposed change needs to fit into whatever the new overall global structure is going to be," he said in quotes published by the Telegraph newspaper.
"If one looks at the concept in isolation... then it's pretty obvious that traditionalists, which includes many players who consider Test cricket as the pinnacle of the game, are not going to be in favour of a change to four days."
Test matches have witnessed a decline in attendances in recent years, throwing the door open to a number of means to engage fans, including the introduction of day-night Tests.
South Africa announced plans to play Zimbabwe in the first four-day Test starting on Boxing Day in Port Elizabeth, as part of their home summer calendar for the 2017-18 season.
Cricket South Africa (CSA) are awaiting approval for the four-day, day/night fixture, which would also be their first home 'pink ball' Test.
However, Irish was concerned that countries trialing four-day Tests on a random basis may lead to confusion and uncertainty around the format.
"If the ICC for example is coming up with a new league structure for Test cricket then how does playing four-day Tests fit into that and what are the advantages and disadvantages of four days, as opposed to five days, in that structure," he added.
"If there are not significant advantages in making the structure and schedule better then why change?
"If there are significant advantages then these need to be understood before decisions are simply made to change the format."
IMAGE: Australia's players relax after a Test match (Image used for representational purposes)
Photograph: Adnan Abidi/Reuters