She is is to undergo a tibial tubercule osteotomy to repair her arthritic left knee with the recovery time set at between 12 to 18 months.
The operation is scheduled to take place in Boston on October 20.
Torres' shin will be broken and shifted to create more room for cartilage to grow around her kneecap.
She already had the first step in the procedure last month, when cartilage was removed from a nonweight-bearing area around her anterior cruciate ligament so it can be transplanted to the area around her kneecap during the next operation.
Torre said: "I think this might make me more motivated to go for 2012, just to prove I can get over this.
"At least I can set this as a goal.
"This is really going be new experience for me.
"It's a little unnerving.
"I was seriously freaked out when I read the literature."
Torres, who's had some more than 20 operations during her career and who has twice come back from retirement, became the first United States swimmer to compete in five Olympics when she made the team last year, at the age of 42, for Beijing - after giving birth to her first child, daughter Tessa.
She became an inspiration to mothers the world over when she anchored two relay teams that won silver medals, and just missed out on the first individual gold of her career, losing to Germany's Britta Steffen by one-hundredth of a second in the 50-meter freestyle.
Torres underwent shoulder surgery after the Games and qualified for the World Championships in Rome in July, but her knee problem hampered her and she finished last in the 50 metres freestyle and was knocked-out in the heats of the 50m butterfly.
After the surgery, Torres will not be able to return to her home in Florida for about five days.
Then, she will be on crutches for six to eight weeks.
The first tentative steps in her rehabalitation will be hooked to a special machine that limits the range of motion in her knee.
Torres said: "I don't know what freaks me out more: having my knee fixed like this or the actual recovery time where I won't be able to train.
"I'm ready to get it done and move on."