Serbian world number two Novak Djokovic has pulled out of the Miami Open with a right elbow injury. The tournament's three-times reigning champion said this today. The injury is the latest setback for Djokovic, who has suffered a drop in form since completing a sweep of the grand slam titles at last year's French Open.Djokovic, who has won a record-tying six titles in Miami, joins world number one Andy Murray on the sidelines of the hardcourt event. Murray withdrew yesterday, also citing a right elbow injury.The 29-year-old Serb was beaten by Nick Kyrgios last week in the fourth round at Indian Wells, marking his second loss to the Australian in less than two weeks.