Red Bull team principal Christian Horner says that the team's RB10 needs pace and reliability ahead of next weekend's season-opening round in Australia.
The team has struggled during pre-season testing as reliability issues have put the reigning world champions on the back foot.
"After testing we quite clearly have a car which doesn't have the ultimate pace, and doesn't have the reliability," he told The Telegraph.
"So they are fairly two fundamental factors that we need to get on top of."
"Pre-season hasn't gone anywhere near as well as we would have liked or hoped, but it doesn't in any way defer our challenge, and make a dent in our drive and our ambition - if anything it only fuels it further."
Horner admits that Red Bull currently don't have the pace to compete with Mercedes.
"To be honest with you, we have no real idea," he said of Red Bull's current placing.
"We know we don't have the pace to challenge the Mercedes teams at the moment, but it's very much a case of see where we are in Melbourne. Then we know the scale and magnitude of what we have to climb.
"We don't even know our starting point at the moment, so it's impossible to make predictions sitting here in Milton Keynes a week prior to the first race. But I have every confidence in the team, and in Renault, that we can make it."
Horner insists that Red Bull can catch-up with their rivals.
"You don't become idiots overnight. We've got a very strong group of people here. There's a real determination. You only have to look at the amount of hours going in. It's massive. Some superhuman efforts are going in to get on top of the issues, to try and ensure we're in as good a shape as we can be in Melbourne and build from there. It's a marathon of a grand prix season, rather than a sprint."