Renault's Cyril Abiteboul has outspokenly refuted Adrian Newey's suggestion that the engine is the only reason why Red Bull is not competitive.
Newey said earlier this month that he saw "no light at the end of the tunnel" with Renault after Red Bull struggled during the season-opening Australian Grand Prix.
It's difficult to have a partner who lies.
In another sign that the relationship is strained, Renault F1's managing director Abiteboul has hit back at Newey's claims, saying the Red Bull chassis is also to blame for the lack of performance.
"Yes, it's difficult to have a partner who lies," Abiteboul told Auto Hebdo when asked how hard it was to hear Newey declare that the only problem was the engine.
"Adrian is a charming man and an engineer without parallel, but he's spent his life criticising engine partners.
"He's too old to change his ways."
Daniel Ricciardo finished sixth in the race, a lap behind the dominant Mercedes pairing of Lewis Hamilton and Nico Rosberg.
Package needs improving
Abiteboul said that analysis of the data from the Australian Grand Prix shows that it is the whole package, and not just the engine, that needs improving.
"Our figures have shown that the laptime deficit between Red Bull and Mercedes in Melbourne was equally split between driveability issues, engine performance and chassis performance," he said in Renault's Malaysian GP preview.
"It's therefore the overall package that needs some help and we have been working with the team to move forward."
The Frenchman is confident, however, that progress will be made in this weekend's race as a result of its aggressive development push.
"We've been particularly aggressive in development and we should see the results a lot more clearly in Malaysia, particularly since we have had the opportunity to refine the PU using the data from Australia.
"Work is still ongoing but even now we are in a completely different place to where we finished Melbourne."
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