Red Bull chief technical officer Adrian Newey has predicted a number of the manufacturers' rivals to perform better his team next season.
After failing to secure Ferrari or Mercedes engines for 2016, Red Bull were left with no other option but to sign a deal with Renault to use Tag Heuer branded power units next year.
And Newey is expecting a tough season for Red Bull as Renault make progress with the new engines.
"If we start the engine with the same power as we have had throughout 2014 and 2015, which I think may well be the case, then we are going to be even further behind," Newey told Motrosport.com.
"I think it is going to be an extremely difficult season for us frankly.
"According to our own research we found some reasonable gains on the chassis side, but the works teams will of course all move forward. Mercedes and Ferrari will move forwards."
Newey is also predicting some of Red Bull's rivals to be more competitive than they are in 2016.
"Toro Rosso, our sister team by having a 2015 Ferrari, will be considerably ahead of this year's Renault power unit," he said.
"I believe Honda, what we have seen, will make a good step. I think their internal combustion engine is a reasonable engine.
"Their problem this year has been that they made the recovery units on the turbo, the MGU-H, far too small. But that is an easy problem to address over the winter."
Newey did not miss a chance to hit out at the Formula One governing body, adding: "So, next year's going to be very difficult for us. It's really down to, I think, what happens next with the sport, for 2017 and beyond.
"Is there a desire from the governing body to allow private teams such as ourselves to properly have competitive engines or not?"