"My back started bothering me in December of 2000 but...gradually it was getting worse and hampering my play until where I couldn't play my game or be myself on court," Pierce told ********************.
"With massage and stretching, it would go away (but) then it would come right back. It was frustrating for me because I wasn't getting better."
The Frenchwoman, who has been plagued by injuries since her emotional triumph at Roland Garros last year, added: "I wasn't playing well. It was taking a lot out of me.
"I knew there was something wrong. I had to stop and see what was going on. I couldn't continue to play that way."
Pierce, ranked as high as number three last year, has failed to win a title since the 2000 French Open and played only 14 matches this year.
The 26-year-old has not played competitively since May - the week before the French Open - when she lost in the first round of Strasbourg.
Despite being sidelined, Pierce said she did not contemplate quitting the sport.
"I've never thought I should pack it in, but it did really get disheartening at times because it's out of your control," said Pierce, who recently split from her fiance, New York Mets player Roberto Alomar.
"I was playing my best tennis, then I had the shoulder injury and came back too soon this year and then the back injury. This year was a good learning experience."