Murray suffered a muscle strain on his right buttock and had to pull out just one hour before his first-round match against Robin Haase.
He will now rest in an attempt to recover for the Paris Masters next week followed a fortnight later by the Barclays ATP World Tour Finals in London.
Murray said: “When I woke up on Tuesday I was really struggling to walk.
“It is something to do with the sciatic nerve and they think I did it in my sleep. Maybe I was sleeping in a bad position.”