Hillary Clinton ‘in hospital’ with blood clot
Mrs Clinton suffered a concussion earlier this month after fainting and falling down.
At the time, she was reported to have had a stomach virus and to have passed out after becoming dehydrated.
Mrs Clinton is due to stand down as secretary of state before US President Barack Obama officially begins his second term in January.
Doctors discovered the clot during a follow-up examination on Sunday, her spokesman Philippe Reines said.
Mrs Clinton is being treated with anti-coagulants. She was admitted to New York-Presbyterian Hospital, where she will remain for the next 48 hours so that doctors can monitor her medication.