Williams, 39, was bidding for a record 24th Grand Slam title at Roland Garros, who finished in the US Open semi-finals earlier this month.
She said the injuries suffered in New York had not recovered enough to compete in Paris.
“I could have done better, but I only saw it in the long run in this tournament.’Can I get through enough matches?’ -So, for me, it’s kind of a clear sign that I think I can’t walk and I’m struggling to walk and I should try to recover,” she told reporters on Wednesday.
Having won three titles in Paris, Williams said, “I definitely felt I needed to walk limping in the second set (first round match).
“I wasn’t limping because I had to focus on walking straight. I always give 100% and everyone knows. If possible it could be more than 100%.
“I’m comforted by that. I think it’s a real injury I don’t want to play because it’s not good for Achilles to get worse. I think it’s the worst one.”
The French Open was originally scheduled to start in May, but has moved to the September start date due to the coronavirus pandemic.
Williams’ withdrawal means that the next chance to qualify for Margaret Court’s 24 major records will be the Australian Open starting in January.