Djokovic 'not sure' about US Open fitness after Olympics nightmare

World number one Novak Djokovic said he was "not sure" about his fitness for the US Open after pulling out of the Tokyo Olympics mixed doubles bronze medal match with a shoulder injury on Saturday.

The 34-year-old Serb could become the first man to complete a calendar Grand Slam since Rod Laver in 1969 when the US Open gets under way on August 30.

The withdrawal in Tokyo came after the 20-time major champio