Sotheby's will sell an example of the RM 027, the watch designed by Richard Mille for Rafael Nadal, in Hong Kong on October 8, when it is bound to attract international attention.

Unlike most tennis stars, Nadal actually wears his watch during matches

The RM 027 Tourbillon was released in a sold-out limited edition of 50 pieces in 2010 at £424,000 ($670,500).

It is common for tennis stars to have a luxury watch endorsement, with players usually seen wearing them in photographs following a match. However, Nadal's watch is unique, designed to be actually worn during the star's high-intensity games.

The watch (right) pictured alongside its contemporaries, such as Hublot's King Power Usain Bolt

To cope with the stress, the watch weighs just 18g and is a mechanical watch, meaning that it requires the movement of the wrist, rather than a battery, for its power supply. This makes it the lightest mechanical watch in the world.

To keep weight to a minimum, Mille has used lightweight materials such as LITAL for the moving components, a carbon-based composite for the casing, and titanium for the baseplate.

As well as superb shock-resistance and performance, the watch also incorporates a tourbillon - a feature rarely seen in sports watches.

"It is an honour that someone like Richard has chosen me as one of his ambassadors. I know that he has worked very hard to be able to create this very special watch. I am sure it will be a special and successful partnership," said Nadal of the watch.

Also starring is a diamond-set Patek Philippe Ref 5073, which will appear at auction for the first time since its release.

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