"I am a 50-50 chance of teeing up on Thursday," the 35-year-old Swede said. "I thought the disc problem was getting better but then it starts to feel a lot worse."
The injury was so bad that Hanson was forced to pull out during the final round of the Greenbrier Classic in West Virginia at the start of this month.
"With seven holes to go we had a rain delay and then after the delay I couldn't get up and move so I had to withdraw," he explained on Monday.
"The big test for me will be tomorrow because if I can play nine holes pain-free then that will be the key to my playing or not."
Hanson, who the BMW Masters in Shanghai in October and the Dutch Open in September, is due to play alongside Japan's Hiroyuki Fujita and American Bill Haas in the opening two rounds at Muirfield.
Dutchman Joost Luiten will be drafted in if the Swede is forced out.
- Sports & Recreation