The 34-year-old Red Bull driver lost the championship lead to Spaniard Fernando Alonso of Ferrari after crashing out in Korea two weeks ago, but claims he has fully recovered and is "110 per cent ready for the fight".
"It's crunch time: we have two races in the space of eight days, at the end of which we'll know the identity of the 2010 world champion," said Webber on his website.
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"It doesn't get bigger than this and I feel 110 per cent ready for the fight," he said.
Although Alonso mathematically has an opportunity to secure the title this weekend, Webber insisted he will not be changing his approach and will be doing his utmost to win.
"Having led the world championship for several races, I go to Brazil second in the points' standings after a rough weekend in Korea. Fernando leads the championship by 11 points, but there are 50 still on the table so there's everything to play for.
"I'm not going to change my approach; I'm going to do my best and let the maths take care of itself.
"More than anything, I need a clean weekend here. The weather forecast looks a bit iffy on Saturday, but it'll be the same for everyone. I can think of no better time to take another victory than now; you can be sure that I'll do everything in my power to achieve that."
Webber, who won last year's Brazilian Grand Prix, hopes his Red Bull car will be as dominant as it has been for most of the season.
"I'm confident that the RB6 will be competitive, although you're always a bit nervous about your pace during the build-up to an event," he added.
"The car has been quick everywhere this year and I see no reason why it should be any different here, but we'll have to wait until the on-track action starts to know for sure."
