Novak Djokovic dropped out of the top four in the world rankings for the first time in a decade on Monday.
The 12-time grand slam champion last week announced that he will not play again this year due to an elbow injury.
Djokovic retired from his Wimbledon quarter-final against Tomas Berdych due to his latest injury setback, which will keep him out of the US Open and the ATP World Tour Finals.
The Serbian has never missed a major tournament in his illustrious career, but that impressive record will end after he ruled himself out of competing at Flushing Meadows.
Djokovic had been inside the top four since July 2007, but slipped down to fifth when the latest rankings were released.
Stan Wawrinka replaces the 30-year-old, who was world number one until Andy Murray took that mantle last November.
Alexander Zverev jumps into the top 10 for the first time, the German leaping to eighth spot.