Mercedes Toto Wolff says Formula 1's new engine platform is "a vision rather than a regulation" which is susceptible to evolve upon further discussions.
The Formula One Group and the FIA revealed yesterday in Paris the sport's 2021 engine, or the foundation upon which the future rules shall be based.
The unit's broad specifications were determined by the necessity to produce a louder, cheaper, simpler power unit, and one which would allow independent engine suppliers to enter the sport.
Wolff considers the concept a first draft, and just one of several possible options.
"The concept sounds similar to what we have now," said the Mercedes boss.
"But it means a completely new development that will mean we are working on two engines at the same time between 2018 and 2020.
"It's a vision rather than a regulation. And it's their vision rather than the manufacturers," he added.
"It is important to define all together what Formula 1 should be in 2021, not just from the point of view of the engine.
"What we have is the starting point of a dialogue rather than something we have agreed to. Certain things are right, but it's not quite there," Wolff added.
Wolff insisted however that Mercedes is not outright against the concept which was presented yesterday, but the manufacturer believes it's a mere starting point.
"I just want to make it clear that there are different opinions," said the Austrian.
"It was a presentation by F1's management, we will now wait and see what is put on the table next week and start a dialogue from there."