Lewis Hamilton has described his race form since Hungary as "shocking", but it seems that Mercedes may have tracked down the underlying cause of the disappointing run of races since the summer hiatus.

"Lewis's results in Abu Dhabi were not what we expected, particularly compared to Nico," team principal Ross Brawn told Formula1.com on Thursday in Austin ahead of the United States Grand Prix at the Circuit of the Americas.

"Nico did a great job, but what was puzzling was that some of the behaviour of Lewis' car wasn't consistent with what we saw with Nico," Brawn went on. "Subsequently we had a very good look at the car and we found that the chassis was quite badly damaged - more than we thought.

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"We knew Lewis had had some excursions over kerbs and things, but when we actually got here and started to strip everything down, the damage was pretty significant," he revealed. "It may even be at a level that was affecting the handling of the car. At what point the cracks became significant is difficult to say, but certainly they were not good."

As a result, Mercedes have elected to switch Hamilton's chassis for Austin in the hope that this will allow the British driver to get back to his race winning form of the middle part of the season.

"I'm just as focused," insisted Hamilton. "Maybe the set-up direction we have been going hasn't been right, though sometimes you can feel like you haven't been in the right place at the right time.

"I'm hoping this weekend to put myself in a better position. I feel positive," he added. "The problem I've had recently is that I've been stuck in a lot of traffic and haven't been able to go past, so it definitely doesn't make the performance seem so good.

"Generally the car is good over one lap, so it's quick enough - quicker than a lot of cars - but sometimes in the race we are not able to show that," summed up Hamilton.