The 2009 Formula 1 world champion ended practice only 16th, 2.1 seconds off the pace.
Rain is expected at various points during the weekend, but Button hopes it holds off long enough for McLaren to work on its problems.
“We need a dry FP3 really because at the moment we’re nowhere,” said Button.
“If we’re where we are now, it won’t be very good. But the car’s definitely better than this.
“We’ve just got to maximise what we have, and we haven’t done that because we’ve tried a couple of different things on the car for ideas for the future and also because of a couple of other issues that we have.
“They haven’t worked, so we’ll go back.
“I have the feeling that it’s wrong in many different ways, so at least we know where to go with the set-up, which is positive.”
Although Button believes the set-up problems can be resolved, he is confused by McLaren’s straightline speed deficit, with both cars around 10km/h down on the works Mercedes.
“The only thing that we find quite strange is that our straightline speed is so far off,” he said.
“We’re not running that much difference in downforce. We’d struggle to run that speed in a straight line without taking the wings off.
“It’s something we need to solve, because we’re losing a lot of time there.”
Button’s day was also hampered by an ERS issue that prevented him from doing any flying laps in practice one.
“It was a bit of a pain, but all OK and all replaced this afternoon,” he said.