Novak Djokovic appeared with a small metal chip on his chest during his victory against Hungary's Marton Fucsovics. At the end of last season, a curious video showing his team preparing in the stands a liquid mixture used by the world number two during a match of the Masters 1000 of Paris-Bercy had sparked many debates.
According to its creators, it would capture body heat to generate a stimulus in the central nervous system of the athlete. But the usefulness of this patch has not yet been scientifically proven.