Red Bull boss Christian Horner has insisted that Formula 1 'cannot afford' to have two of its engine manufacturers continuing to struggle.
The Milton Keynes-based outfit have seen their performances decline since V6 turbo engine regulations were introduced last year, which led to open criticism of engine supplier Renault.
McLaren-Honda have had to contend with issues of their own, which Horner believes is damaging the sport's image as two of its four manufacturers are well off the pace.
"I don't think Formula 1 can afford for Honda and Renault to be in the situation that they are," ESPN quotes the Red Bull chief as saying.
"We had the new president of Honda [in Austria] and I don't think we put a great show on for him. And for Renault again, it is not a great encouragement for them to commit further to the sport, when the penalties that we are imposing, the public embarrassment there is over engine failure.
"I think we need to look at it for sure, and don't get me wrong, quite often I am perceived as moaning or complaining about Mercedes, but they have done a super, super job. They have interpreted the rules and done a better job than anybody else."
Red Bull currently have 55 points this season, compared to runaway leaders Mercedes who have 328 to date.
