The MP4-26 has been beset by problems in testing
Lewis Hamilton has echoed team-mate Jenson Button's concerns over the new McLaren car, saying the MP4-26 is far from ready to mount a title challenge.
Since its belated unveiling last month, the new car has had a number of problems, including at this week's final pre-season testing in Barcelona.
"Do I believe I have a car to win the world championship at the moment? I don't. No," said Hamilton.
"But that doesn't mean it won't become a world championship-winning car."
On Tuesday, Jenson Button said he believed McLaren would not be able to challenge rivals Red Bull and Ferrari at the season-opening Australian Grand Prix on 27 March.
Button was 0.366 seconds behind Red Bull driver Mark Webber's best time in testing at Barcelona but his time was limited in the morning session because of exhaust problems.
Hamilton was fourth behind world champion Sebastian Vettel on Wednesday's second day after reliability issues confined him to spells in the garage.
We definitely have several issues that are not as easy to rectify as we had hoped
The 2008 world champion was halted by a recurrence of the hydraulics problem that affected Button at the last test and then an exhaust failure before lunch.
A further exhaust issue then confined him to another prolonged spell in the garage in the afternoon before he returned to the track to set his best time of 1:22.888 - still 1.023 seconds behind Vettel's best time.
But although the McLarens will be at a disadvantage to the likes of Red Bull and Ferrari when the season starts in Melbourne, Hamilton is trying to remain upbeat.
"It has been a tough day in the sense that we've not done enough miles," he added.
"I came here hoping to do more laps, to get in a good 100-odd laps, to get in a race distance. Usually at this time of the year this is when we come with pit stops and one or two race distances a day, but we were nowhere near even completing one.
"So it was a bit on and off, it wasn't a great day for us, but in terms of how the car felt there was an improvement with some of the upgrades we have. So that is at least a positive, it's not all negative.
"I can do qualifying, no problem; can do practice, no problem.
"But in terms of how long we can go in terms of reliability and our true pace, that's an unknown factor for us because in the time we have had we've not been able to maximise things.
"That's no-one's fault, just issues you have in testing, and this is testing, this is what it's all about, finding where your weaknesses are so you can build on them and fix them.
"We've been focusing on those, but we definitely have several issues that are not as easy to rectify as we had hoped.
"Looking at how the car has developed over the winter and seeing how it has come out, I was really, really excited getting into it thinking we really had hit the nail on the head.
Hamilton was in demand for autographs at the Circuit de Catalunya
"But we've missed that nail a little bit, although it's not like we don't have any other opportunities to get it right.
"From this, the improvements we've had, it's something that can grow to be better, so as long as we keep pushing in the right direction with the development, and the new things we have coming several races down the line, hopefully they will enable us to close the gap and compete for wins."
Hamilton is also adamant that despite the problems, the chances of winning the 2011 world title have not completely disappeared.
"I have every belief in my heart that I can win many, many more world championships," he added.
"So I'm definitely not shutting the year off. Everything is still to play for.
"As long as we keep pushing in the right direction with the development, and the new things we have coming several races down the line, hopefully they will enable us to close the gap and compete for wins.
"If we pick up a good few points in the first few races, then we won't be miles behind.
"Say for example we were able to be in the top five for the first three or four races, get those points, and then if we happen to have a car capable of winning, then it would still be possible.
"I'm ready, and when the car is ready I will be at the front and I will win races, but whether that will happen, we'll see."