LOS ANGELES (KTLA) -- Tennis star Serena Williams had "emergency treatment" at a Los Angeles hospital Monday for a blood clot in her lungs, People Magazine reports.

Williams' spokeswoman, Nicole Chabot, told People that the treatment was for "a hematoma suffered as a result of treatment for a more critical situation."
Chabot said the 29-year-old suffered a pulmonarembolism last week.

"Doctors are continuing to monitor her situation closely to avoid additional complications," Chabot told People.

Williams is reportedly being treated at Cedars-Sinai Medical Center.

She posted to her Twitter account Tuesday night, saying only, "Tough day."

The tennis ace attended Sunday night's Elton John AIDS Foundation Academy Awards Viewing Party.

The embolism was discovered after Williams returned to Los Angeles from New York for a doctor's appointment for issues with her foot, according to Chabot.

Williams has had two operations since she cut her right foot on some glass at a restaurant in Munich last July. Williams was celebrating her win at Wimbledon.

She has not played a competitive match since, sitting out both the U.S. and Australian Opens.

Williams has won 13 Grand Slam titles. Her current world ranking has slipped to 11th due to inactivity.