Red Bull boss Christian Horner made his frustration with Renault clear once again after Daniel Ricciardo finished a lapped sixth in the Australian Grand Prix.
Horner insisted after the race that the engine masked the true potential of the RB11.
The engine is just quite undriveable.
"It's been a tough weekend for Renault," he said. "The engine is just quite undriveable. You can see and hear that from the comments the drivers are making.
"The most clear evidence is that off the start Daniel got a reasonable initial start and then driveability comes in, and you can see the holes that are in the power delivery, so a lot to be done."
Elaborating on the symptoms he said: "I think it masks so many things regarding corner entry, corner exit, degradation, slip control of the tyre. You're not able to drive the car properly.
"So you then start moving your brake balance around to try to compensate, so you are so far away from optimum. You start to lose temperature in brakes, and then the tyres aren't working as they should. It's a spiralling effect."
Change must come quickly
Horner insisted that Renault has to have solutions in hand.
"They need to have, and they need to quickly.
"You can see that Ferrari made a step forward, Sauber all respect to them, but I doubt they found much on their chassis from last year to this year because most of it's the same, same front wing, same rear wing, but you can see Ferrari have made a good step.
"Renault at this stage appear to have made a retrograde step."
"It's frustrating that effectively we are further back than where we were in Abu Dhabi in both power and driveability."
Asked by Motorsport.com where the unravelling Red Bull/Renault relationship would develop from here, he said: "Obviously after this weekend it's important that we regroup with Renault and we try and offer support where we can, because obviously they are in a bit of a moment and need to understand things quickly.
"Across the four cars we've had two engine failures, one within five laps, and a whole bunch of driveability issues, so it's not the start that Renault can afford to have."