Mercedes boss Toto Wolff says he expects a tougher contest from Ferrari next year to defend its place at the top of Formula 1 having seen the Italian squad gradually erode the deficit over the course of 2015.

Despite the reigning F1 champions still holding an edge in qualifying, with both Nico Rosberg and Lewis Hamilton over half a second clear of Sebastian Vettel over a single hot lap at the Brazilian Grand Prix, Ferrari have gradually been closing in on its rivals in terms of race pace.

This pressure has seen Mercedes opt for conservative strategies to combat the threat of Ferrari and Wolff believes the trend will continue into next season which he says his team must prepare for.

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"I am anticipating a robust challenge from Ferrari because they have done some clever moves, and they have definitely caught up," Wolff said. "You can see that even towards the end of the race today Sebastian was not very far away, when Lewis and Nico pushing flat out biggest gap was seven seconds, that is not a clear-cut, dominant race win. I think we will have a situation where Ferrari will be a very important competitor."

In Brazil, Ferrari team principal Maurizio Arrivabene confirmed his squad has made huge strides forward with its power unit - but brushed off Niki Lauda's comments that they have matched Mercedes - and is expecting Ferrari to make similar gains with its chassis developments in 2016.

Vettel is the only driver in 2015 to beat the dominant Mercedes duo of Rosberg and Hamilton, with three wins in Malaysia, Hungary and Singapore.