MIAMI - Rafael Nadal withdrew from the Miami Masters prior to his scheduled semi-final against Andy Murray on Friday with a knee injury. “So sorry for my fans, those here at Miami and those around the world,” the Spanish world number two wrote on his Twitter account. “My knee won’t let me play today.”

It’s a blow for Nadal with the start of the clay court season looming.

Nadal is playing in only his third tournament of 2012 having fallen in the semi-finals in Doha, finished runner-up to Novak Djokovic in January’s Australian Open final and making the Indian Wells Masters semi-finals last week.

His last title came at the French Open last year. “Rafael Nadal has been forced to withdraw from today’s match at the SEOpen due to a knee injury,” a posting on the ATP’s Twitter feed said. “Andy Murray advances to the final.”