McLaren's Martin Whitmarsh has openly admitted the MP4-24 is not as competitive as the team was hoping it would be at this point of the pre-season.
The team has failed to be close to the top of the timesheets in testing, with both Lewis Hamilton and Heikki Kovalainen failing to make an impression, leading to suggestions that the team had problems with the car.
On Friday, Whitmarsh confirmed that was the case, admitting the team has found a performance shortfall that it is working hard to rectify.
"Initial testing of MP4-24, which first ran with an interim aero package, went in accordance with our early developmental expectations," said Whitmarsh.
"This week the car has run in Barcelona with an updated aero package, as we had always planned it would, and a performance shortfall has been identified that we are now working hard to resolve."
When asked if the car was fast enough at the moment, he added: "Not at the moment - and certainly not by our team's extremely high standards.
"But Lewis is the reigning world champion, and he became world champion in one of our cars.
"So anything less than success at that level is naturally regarded as unsatisfactory by us, by our partners, by the media and by the fans. Having said that, McLaren has started 648 grands prix. We have won 162 of them and have recorded 431 podium finishes.
"We are proud of our record and have faith in our engineers' ability to work hard to get MP4-24 into a position to add to that record. They are already engaged in doing exactly that."
Mercedes-Benz motorsport boss Norbert Haug said the problems will need time before they are solved.
"We are definitely not where we want to be. We will continue our test programme next week at Jerez for another four days. But it will take time to improve," Haug said.
Whitmarsh, however, said the team will be working flat out to rectify the situation and he is convinced the problems are fixable.
"It is a combination of factors," said Whitmarsh of the car's problems. "Our Mercedes-Benz engine is strong - we saw that last year - so MP4-24's performance shortfall is clearly chassis-centric.
"Inevitably, in 21st-century Formula 1, it is a car's aero aspect that confers the greatest pluses and minuses to its overall performance package, and that would appear to be the case with MP4-24. But Formula 1 engineers can do great things when the pressure is on.
"Speaking to them today, I was struck by their resolute determination to address MP4-24's issues in record time. In fact, it is that kind of resolute determination, coupled with expertise and experience of ultra-high technology and the ability to work accurately and quickly under pressure, that makes Formula 1 the great sport and the tremendous engineering challenge it is."
He added: "Many times in Formula 1 history have successful teams started off with a car that was not working as well as they had hoped it would, and many times have those successful teams engineered their way back to the front of the grid in impressively short order. That is what we aim to do. In fact, that is what we are already doing."