Button, Hamilton gear up for crisis talks with McLaren after Silverstone debacle
Both former world champions are believed to be devastated after performing poorly at the Silverstone, finishing eighth and tenth.
Both openly admitted the Melbourne winners are no longer Formula One's top dogs, or even at the top table, but were the seventh-best team on the day.
"It is going to be a somber meeting but we will all be aggressive, I am sure, trying to improve this car. We don''t have the pace of the top three teams - at the moment we are racing Williams, Sauber and Force India," The Daily Mirror quoted Button, as saying.
"But if the Williams and Sauber had a good day at Silverstone, they would have beaten us, so we have a lot of work to do. We are fourth in the constructors and we will have to sort that out. We can''t end the season here - or worse," he added.
"We are McLaren. We have got to improve," he said.
Asked whether the car had a ''fundamental design flaw'' Hamilton replied: "I''m not using those words, I''ll let you use those words. I feel I know what the problem is but unfortunately it''s too big a change for us to do in a season. It''s something you need to do in the next car."
"So I am already speaking to them about how we can make the next car better. And in doing that and talking about the next car we also improve this car as well," he added.
"You''ve got to look at the cars in detail, just look at them. Ours look different to the others. That''s a significant difference," he said.