People claims that the tennis star fell ill recently and underwent treatment earlier this week in Los Angeles Cedars-Sinai Medical Centre.
"Monday Serena Williams underwent emergency treatment at Cedars for a hematoma she suffered as a result of treatment for a more critical situation," a spokesperson for the 29-year-old said.
"Last week, Serena suffered from a pulmonary embolism [a blood clot in the lungs] which was discovered upon her return to LA. She had been in New York for doctor appointments for the ongoing issues with her foot."
They added: "Doctors are continuing to monitor her situation closely to avoid additional complications."
The Wimbledon champion previously injured her foot after stepping on glass outside of a restaurant in Germany last year.