Interesting that TWE on facebook says "Noticed this mysterious HEAD racket, next to Novak Djokovic´s bag?"
They specifically said "HEAD" racket, and they've play tested it. And I thought I saw a HEAD stencil on the strings during the change over. But I noticed it didn't have the same grip/overgrip on it, so I really think that he wasn't using it, but placed it there to get attention. The black racket was placed next to one of the current rackets, and neither one looked like it was touched for the whole match.