Mercedes Formula 1 chief Toto Wolff says the team "can take nothing for granted" despite being able to wrap up both the drivers' and constructors' championships at this weekend's United States Grand Prix.

Victory for Lewis Hamilton last time out in Japan has put him 59 points clear of Ferrari's Sebastian Vettel with four races and 100 points remaining, while Mercedes sits 145 points ahead in the constructors' standings.

Mercedes will wrap up the teams' title this weekend if both Hamilton and teammate Valtteri Bottas finish inside the top four, while Hamilton will take his fourth drivers' crown if he moves an additional 16 points clear of Vettel.

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Nevertheless, Wolff has stressed the importance of Mercedes staying focused and committed as it bids to complete a fourth straight title double.

"Still four races to go and 100 points to score: we can take nothing for granted as we fly to Austin this week. We approach every race with a healthy dose of scepticism rather than wishful thinking, and our focus must be on making sure we score every point within our reach this weekend in Austin," Wolff said.

"Since we began the final flyaway leg of the season, we have seen a strong points swing in our favour in both championships. Good fortune has played its part, of course - and we have put ourselves in the right position to make the most of the opportunities that have come our way. But nobody within the team is allowing those good results to disguise the challenges we have faced.

"We returned from those races with a lot more understanding of our car and of the reasons for the performance swings we have experienced this season. Some of that understanding is already being applied to the final races, some of it will flow into next year's project.

"But the bitter taste of our defeat in Malaysia once again confirmed that the tough days are the ones when you learn most - and when you lay the foundations for future success."