Novak Djokovic has apologised to fans after retiring during the Cincinnati Open final against Andy Murray.

The Serb was forced to withdraw with a shoulder injury at 3-0 down in the second set, having lost the first 6-4.

"I apologise to the tournament and the people who came to see this match," Djokovic said.

"I could not serve and I could not play forehands. It’s unfortunate that I have to finish this way."

"I could not beat a player like Murray today with one shoulder," the world number one added.

It is only the second encounter Djokovic has lost this season, having won his other 57 matches.