Williams, 39, would have met Tsvetana Pironkova in the second round today.
After going out in the semifinals of the US Open a few weeks ago, Williams withdrew from the gravel tournament in Rome.
- I tried, everyone knows that I always give one hundred percent and even more if possible.
But you do not want to risk anything when it comes to this type of injury.
If it gets worse, it's one of the worst injuries you can have and I do not want to end up there.
I now want to focus on being injury-free, the star said during a press conference.
CLIP: Serena works with performance requirements (September 29)
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Serena works with performance requirements: "Can not win every single ball" Photo: TT News Agency