The Briton is not happy with the reliability issues that have hurt the F1 team last season.
Button's worry over McLaren
Jenson Button has acknowledged that he and McLaren-Mercedes have a lot of work to do if they are to be contenders for the world championship when the new season begins in Australia at the end of the month.
McLaren's new car, the MP4-26, has failed to impress in testing in Spain thus far and, with only next week's final five-day test at Barcelona to come, the British team are looking unlikely to be a major factor at the front in Melbourne on March 27.
Button, the 2009 world champion, who has won for the past two years at the Albert Park circuit, said: "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 days and hopefully everything's going to run sweet at the next test, and we get a lot of laps in and we can improve the base that we have.
"There's a lot still to extract from this car that we haven't because we just haven't had time to do it, we haven't got everything together yet, so we don't really know where we are compared to the competition.
Due to the mechanical problems the Briton referred to, the team have done few miles compared to the Red Bull and Ferrari cars, who have looked the most impressive in testing to date.
The 31-year-old admitted: "When I first jumped in it [the car] the first reaction was not 'Wow, we're going to blow everyone away'.
"I don't think anyone would have felt that because it's got a lot less downforce, the [Pirelli] tyres are working very differently to the previous [Bridgestone] tyre.
"But there's nothing that really scares me about the car in a negative way, so there's a lot we can improve with this car through general set-up work."
McLaren finished second in last year's constructors' championship, and Lewis Hamilton, the 2008 world champion and Button's teammate, was in contention for the drivers' title until the final round in Abu Dhabi.