Formula 1's long-life engine rules will get more than twice as arduous for manufacturers beyond 2019.
A few weeks ago, after a long period of negotiations, changes to further converge performance and cut costs were finally agreed.
At the time, the FIA said that cost reduction will be possible through a "progressive reduction of the number of power unit elements per driver per season".
Currently, drivers can use five engines per season, but Germany's Auto Motor und Sport says that by 2019, that number will drop dramatically to just two, irrespective of the size of the race calendar.
When asked if that will even be possible for Mercedes, Ferrari, Renault and Honda to achieve, FIA race director Charlie Whiting said: "I am confident they will succeed, because the manufacturers themselves are confident and agreed to these numbers."
The 2016 championship continues this weekend with the Monaco Grand Prix.
