Cricket's official lawmakers have urged the ICC to stick with five-day Tests and knock back any move to shorten the format.
The ICC's cricket committee are expected to meet this year on a proposal to shorten all matches to four days, in a move strongly opposed by players.
Under an idea supported by numerous administrators, it's claimed shortening matches to four days would not change most results and free up the calendar.
However players claim it would cheapen the Test format, run the risk of having more draws and largely dent the impact of spinners on wearing pitches.
High-profile Australian players Tim Paine, Josh Hazlewood and Nathan Lyon have been among the vocal critics, with the latter labelling the idea "ridiculous".
Globally, Sachin Tendulkar has also warned against the move, as has powerful India captain Virat Kohli, England counterpart Joe Root and the international players' union.
The Marylebone Cricket Club's world cricket committee - which includes Ricky Ponting and Shane Warne - advised against a four-day Tests as recently as 2017.
And they reaffirmed their position on Monday after further discussions.
"MCC has noted the recent discussion regarding the future of Test cricket and the ICC's desire to debate the introduction of four-day Test cricket to replace the current five-day format in the World Test Championship from 2023," a statement read.
"The MCC cricket committee and MCC world cricket committee have recently discussed the issue.
"Although they can see some benefits that four-day test cricket could bring, both committees believe that test cricket should continue to be played over five days."
Under cricket's structures, the MCC set the laws of the game while the ICC determine how international matches will be played.
Five-day Tests have been in place since 1979, with games played over varying distances previously.
However, in the past two years, approximately on 40 per cent of matches have reached into a fifth day.
Trials of four-day matches were approved by the ICC in 2017, with Zimbabwe and Ireland among the two teams to feature in those games.
A third could also be played next summer when Australia host Afghanistan.
In the trials - which have only been played in matches involving minnow - days have been expanded to 98 overs per day.