"I have decided not to play in Bastad next week because I am still not at 100%," the World No.1 said. "I want to be in top physical shape to compete and I expect to start training next week. I want to thank all of my fans in Sweden and everyone associated with the Collector Swedish Open for their support and understanding. It was my favorite spot to play last year and I am deeply saddened I cannot return.
"But there is always next year, and believe me, I look forward to it."
Williams' victory in Bastad last year was something very special - for all the Grand Slams and Premier titles she has won in her career, it was her first - and still her only - International-level title.
Take a look back at highlights from the final and trophy ceremony from last year here: