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McLaren have admitted they are off the pace and have "a lot of work to do" to become competitive.

Jenson Button was 2.386 seconds off the pace in second practice at the season-opening Australian Grand Prix.

Team boss Martin Whitmarsh said: "It was one of the hardest days I can recall. We were lacking overall grip. We had understeer, poor ride.

"So a very difficult day, one where we didn't go forward during the day, so that's a bit of a concern."

Button said he "agreed with Martin", adding: "I think there is a lot of work to do.

"It is definitely not the place where we wanted to start the season but all is not lost yet and we are very good at turning it around.

"We have found very difficult times before and I don't think we're as bad as that."

McLaren have blamed their poor start to the season on their inability to get the best out of a car on which they have made major changes since last season.

Whitmarsh said: "There is a lot we still need to learn about this car. But we have struggled frankly to quite understand how it is performing - understanding the tyres and the car."

While most other teams have decided to build an evolution of their 2012 cars, McLaren - who had the fastest car for most of last year - have decided to take a more radical approach.

The decision was based on their belief that there would be more development potential in the car if they made bigger changes.

"We took the decision to make a lot of changes and knew that to some extent that would put us back a little bit, but we were hoping to get on top of that before the first race," Whitmarsh said.

"As of today we are still undoubtedly struggling and that is something we need to gather good information on and work through it this weekend."

Sporting director Sam Michael said: "Definitely, we are not where we need to be at this point in time.

"We made quite a few changes to the car over the winter, and we still believe they will be good for the course of the season.

"But we are still unoptimised in the areas we need to be, which comes from our own knowledge of where they are not as good as what they should be.

"So we still have some work to do on the car. But it's a long season."

He added: "The intention was to have a winning car right here in Melbourne. But, even if we don't, at least over the course of the season it offers a lot more development potential.

"And we can see that as well in the factory. We can see the areas it is improving. We are just not quite there yet."