Tennis star Serena Williams underwent ''emergency treatment'' after doctors discovered a blood clot in her lungs, People magazine reported.
Spokeswoman Nicole Chabot told the magazine that Williams ''underwent emergency treatment for a hematoma suffered as a result of treatment for a more critical situation.''
Williams suffered from a pulmonary embolism last week, Chabot said. The 29-year-old Williams is being treated at a Los Angeles hospital.
''Doctors are continuing to monitor her situation closely to avoid additional complications,'' Chabot told the magazine.
The winner of 13 Grand Slam titles, Williams attended Sunday night's Elton John AIDS Foundation Academy Awards Viewing Party.
On Tuesday night, Williams posted on her Twitter account ''Tough day.''
Williams has been sidelined by two operations on her right foot after cutting her foot on glass at a restaurant, and has not played a competitive match since winning Wimbledon on July 3.
Chabot also told the magazine that the embolism was discovered after she returned to Los Angeles from New York ''for doctor appointments for the ongoing issues with her foot.''
