Rafael Nadal withdrew from the Cincinnati Masters on Wednesday, organisers said, just a day after his withdrawal from the Toronto tournament had already cast doubt on his fitness for the US Open.

The 35-year-old Spanish star has been suffering from a left foot injury since his semi-final exit at the hands of Novak Djokovic at the French Open in June.

Nadal, level with Djokovic and Roger Federer on 20 Grand Slams, is hoping to be fit for an assault on a fifth US Open title when the final Grand Slam of the year starts on August 30.