F1 legend Alain Prost doubts struggling engine supplier Renault can catch dominant Mercedes in 2015.
Having faltered at the start of the new turbo V6 era, Renault - whose prominent F1 partner is the outgoing world champion team Red Bull - can upgrade its 2014 engine to the tune of 48 per cent under the existing 'freeze' regulations.
But Mercedes' rivals are arguing for the 'freeze' to be further relaxed.
A total freeze as it is now is synonymous with stagnation, but just opening up everything is too expensive. A good compromise is needed.
"It will be hard for them (Renault) to catch up with Mercedes," quadruple world champion Prost, a Renault ambassador, told Germany's Auto Motor und Sport.
"But it also depends on whether there is a change in the development timetable (the engine freeze) by the FIA.
"A total freeze as it is now is synonymous with stagnation," Prost argued. "But just opening up everything is too expensive. A good compromise is needed.
"We should not make a final judgement about Renault until next year," he added.
At the same time, Prost thinks it is understandable that Renault fell behind Mercedes just as the rules changed so dramatically, given Red Bull's run of title domination at the end of the V8 era.
"It was almost inevitable that Mercedes would start with an advantage," he said.
"Last season I was saying that it would be hard to beat them as they started developing much earlier.
"Renault was always defending a world title in the last years," Prost explained, "while Mercedes was able to concentrate fully on the new project."