Murray, who recently underwent back surgery, has lost his third place in the ATP list to David Ferrer after being unable to defend points gained at last year's Shanghai Masters.
The Wimbledon champion, who has been ruled out of the rest of the season but plans to return for the start of 2014, will hope to avoid slipping any further during the rest of the year.
Juan Martin Del Potro, Tomas Berdych and Roger Federer are all lurking behind Murray in the ranking list and good results for them in the coming weeks could see the Scot head into the Australian Open as the world number seven.
Were he to be seeded seventh, Murray would be at risk of playing Rafael Nadal or Novak Djokovic in the quarter-finals in Melbourne.
At the top of the ranking list, Nadal has stretched his lead over Djokovic despite the Serb's title triumph in Shanghai. As defending champion, Djokovic could only keep his points total for the rolling 12-month period stable whereas Nadal, who was injured this time last year, added points to his tally with a run to the last four.
In the women's rankings, Heather Watson has slipped out of the world's top 100 for the first time since Wimbledon 2012.
Her miserable, illness-affected season continued last week in Osaka where she was the defending champion. Her first-round defeat saw her lose a stack of points and, as a result, she slips down to 133rd in the WTA rankings.
Watson, who plays in the Luxembourg Open this week, is now only the British number three. Johanna Konta is the new British number two. She is ranked 115th.
Laura Robson remains the top-ranked Briton but she has dropped to 46th in the latest list.
Serena Williams remains the world number one and is already guaranteed to finish the year in that position.