Button fears he is too slow
Button has struggled over one lap in the last four grands prix, and that has compromised his race, coming away with just 11 points in total from Britain, Germany, Hungary and Valencia.
After finishing 17th in practice around the Spa circuit on Friday, just under a second off the pace set by Lewis Hamilton in his McLaren, a downbeat Button said: "I'm not 100% happy with the car at the moment.
"We definitely don't have a tyre temperature issue here. The tyres are working. They're very hot.
"I'm sure it's down to some of the things we've done to the car to help with that, but also the asphalt is quite abrasive.
"In fact, a lot of people are struggling in their long runs with overheating, so that is something to watch out for here.
"Overall our long-run pace is reasonably competitive, but we still have to work on our qualifying pace because we're not that strong over one lap.
"We're not on the pace of the Red Bulls and some of the other teams over one lap, whilst the balance of the car is also not great, so there is still a lot of work to do before we are competitive."
The likelihood is Button's lead over Mark Webber and Sebastian Vettel, currently 20.5 and 25 points respectively, will be eroded this weekend. Button added: "This is the perfect circuit for a Red Bull car, so we have to hope we can be as close as possible and nibble some more points off them.
"Obviously, this circuit is fun to drive. I just have to hope our car is this weekend because the circuit is not the best for it, but we'll do the best job with what we have."
Team principal Ross Brawn has also conceded the team have plenty of work ahead of them if Button and team-mate Rubens Barrichello are to have any hope of challenging at the front.
"We're not experiencing any issues with tyre temperatures so far which is positive, and it's good to see our hard work in this area starting to pay dividends," assessed Brawn.
"But there is still some way to go to maximise the set-up of the car to the requirements of both drivers, so it will be a busy hour of practice on Saturday morning to get ready for qualifying."