The World Motor Sport Council, currently in the middle of a three-day meeting in Dubrovnik, is expected to confirm that as from 2014 first practice on a Friday will run for two hours rather than 90 minutes.
The idea is to give the teams' reserve drivers an opportunity behind the wheel they would ordinarily not obtain throughout the course of a campaign, especially with the annual young driver test to be made redundant.
But McLaren boss Martin Whitmarsh and Mercedes counterpart Ross Brawn have both revealed they are extremely unlikely to use their reserves.
"From McLaren's perspective it's not something we'd necessarily want to do," said Whitmarsh.
"I can understand the view of some in that it's very difficult for young drivers, there's very little testing and it's a way of encouraging them.
"Oddly, I think it will work against the smaller teams because at the moment they have a unique opportunity to sell FP1; many do and it's a surprisingly important revenue for some of those teams.
"If every team has that opportunity then the value of what some of those smaller teams are able to sell is reduced.
"Unless the regulations require you to have a young driver, or whatever the definition, probably none of the big teams would do it.
"From our perspective we'd go to work thinking how we can use that half an hour to do aerodynamic testing.
"Ultimately we would not be doing performance testing in terms of lap time, set-up, we'd be doing a whole range of component changes and just data logging on the straights.
"So it probably wouldn't have the desired effect, although you'd have to look at the precise detail of what they define.
"As is often the case, quick ideas in Formula One have unintended consequences.
"The teams figure it out for themselves how to exploit it to their best advantage, which is not necessarily aligned with the original intention of such an idea, so I think you'd have to think about it carefully."
Brawn has made it quite clear Lewis Hamilton and Nico Rosberg would not be replaced as it would pose difficulties.
"For us, we'll still stick with the race drivers," said Brawn.
"One of the main changes is an extra set of tyres for the first half hour, which I think is a good move, but the ability to change drivers during a session is actually not easy.
"If you've drivers with too much variance then it's not such an easy thing, but it's doable.
"It's not something we would consider because we need all the time in the car with our two race drivers.
"There will be a point on the grid where it is more attractive to some teams, but certainly not for teams that are fighting for races and fighting for championships."