The two McLaren drivers had a lot of reliability issues with their new car during the first three winter tests and as a result didn't get enough mileage under the belts. With only one more pre-season test to come in Barcelona, McLaren will have their work cut out for them.
Button admits he had concerns about the MP4-26 pretty much from the word go.
"When I first jumped in the car my first reaction was not 'wow, we're going to blow everyone away'," Button told Press Association Sport.
"But then I don't think anyone would have felt that because the car has a lot less downforce and the tyres (Pirelli) are working very differently to the previous tyre (Bridgestone).
"There's nothing that really scares me about the car in a negative way, so there's a lot we can improve through general set-up work.
"This year, at the moment, we've had some issues in testing in terms of getting parts to the circuit and a couple of reliability issues.
"So we've not done as much running as we would have liked, which has hurt our set-up work.
"But we do have four more days and hopefully things are going to run more sweetly at the next test, we get a lot of laps in, and then we can improve the base we have."
Team-mate Hamilton concedes that they probably left their car launch a little too light.
"The team are aware of it, and of course we'd love to have had more mileage, but there is a real balance," he said.
"We left it (unveiling the car) a bit later, not because the car was late, but because we wanted a week or two more to develop it, and perhaps it's not played right into our hands.
"We've good things in the pipeline, and we definitely improved in the last couple of days' testing, doing 107 laps on the final day at the last test.
"We've not done the mileage at the beginning, but hopefully we can pick up on reliability, and that the downforce is on its way."
The 2008 World Champion added that there were some similarities between the 2009 car and the 2011 model when it comes to downforce.
"The '09 car was terrible as it was hopping, three-wheeling through corners, locking up, and it had no downforce," he said.
"This car doesn't lock up, it doesn't three-wheel, and it handles really nice, better than last year's car, but it just doesn't have as much downforce.
"Because the regulations have changed, it's a similar downforce level to '09.
"We have a little more, but it's not far off, so it feels weak in that area. Hopefully we've more downforce coming onto the car."
Source: http://www.planetf1.com