Jenson Button says that Brawn has to stop blaming cool temperatures and start looking at other causes for the team's recent loss of pace.
The World Championship leader, who holds an 18.5-point advantage over Mark Webber going into the summer break, says he is mystified as to why his Brawn GP car is not performing to the same level it was when he dominated the start of the season.
"I don't know what it is, but I don't think we can blame the weather," he told the BBC.
"It is a bit colder today than it was Friday but we have got to be looking in other areas than that."
Button called upon his team to urgently solve the problems that caused his rear tires to grain so badly in the Hungarian Grand Prix, where he finished a distant sixth.
"We have had two different updates on the car but they shouldn't unbalance the car in any way," Button said. "You can say that the other teams have improved their cars for sure. The Red Bull is a lot quicker and obviously McLaren, Ferrari and Williams have stepped up their game. But our car is not what it was to drive a few races ago.
"It's not that we've got the same paced car and everyone has overtaken us. Our car is not driving as it has done from the start of the season so there is obviously an issue, but the good thing is there is a break before the next race for us to try and solve it."
The Briton admitted that his race had been one of damage limitation as it quickly became clear that he did not have the pace to fight for victory.
"It was damage limitation in the end, but it wasn't supposed to be," he said. "Friday our pace was good on the option tire. Everybody else was struggling with rear graining and we had a very good rear end. We didn't grain at all like normally we do on the rear tires.
"Today my tires were destroyed after four laps, my tires were destroyed and I couldn't stay with the cars in front.
"Obviously the plan was stay closer to the cars in front and when they pitted I could go a lot longer but I don't know why we grained the rear tyres today."