People magazine quoted her spokeswoman as saying she had “emergency treatment for a haematoma she suffered as a result” of that treatment.
“Doctors are continuing to monitor her situation closely to avoid additional complications,” she added.
Williams, 29, has not played competitively since winning Wimbledon in July 2010 because of a foot injury.
That occurred when she cut her foot on glass in a restaurant when celebrating her Wimbledon triumph and it prevented her going for a third successive Australian Open triumph in January this year.
Williams, the current world 11, can count four Wimbledon titles among her 13 Grand Slam victories, making her the sixth most successful Grand Slam player in women’s tennis history.
She has won all four of the world’s top tournaments – the US, French and Australian Opens and Wimbledon – and also won a gold medal at the 2000 Olympics in Sydney.
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Serena Williams Undergoes Emergency Blood Clot Surgery