Red Bull has labelled Renault's performance in Formula 1 as 'unacceptable', and called on the French car manufacturer to make changes.
The reigning champion endured another frustrating race in Austria, with Sebastian Vettel's afternoon wrecked by a power unit failure and Daniel Ricciardo only managing eighth.
And with the team having set Renault a deadline of this weekend to show what its potential could be, Red Bull boss Christian Horner did not hold back on Sunday night when asked about his feelings on the situation.
"It's frustrating that we're in the situation that we are," he said, when asked by AUTOSPORT for his feelings on Renault's performance.
"We've obviously had a lot of success with Renault.
"We've won all the races and all the championships that we've achieved with Renault power. But the situation just isn't improving at the moment.
"The reliability is unacceptable. The performance is unacceptable. There needs to be change at Renault. It can't continue like this. It's not good for Renault and it's not good for Red Bull.
"We need to work together as partners. There will not be another engine in the back of the car next year, but we want to be competitive and we want to run at the front."
When asked to clarify what he meant by changes at Renault, Horner said: "Something needs to happen because whatever's being done there at the moment isn't working.
"It's not our business, it's not our responsibility. We're the end user and it's just frustrating that it's not where it needs to be at the moment."
Renault deputy managing director Rob White said he empathised with Red Bull's frustrations at the situation, but was adamant that a path of recovery had been mapped out.
"The anxiety that Christian feels, and the frustration he feels after a result that is not at the full potential of the performance of car and power unit, is completely understandable and shared by us," he said.
"But we are completely committed to making progress as fast as we possibly can - and I think we have shown signs of progress before now and we remain sure of where the expectations of Red bull and Christian lies.
"We know what is expected of us and individually and collectively we must buckle down in the right direction.
"This is a process that is completely shared with Red Bull, and the objectives are known and understood."
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