US Secretary of State Hillary Clinton has been admitted to hospital in New York with a blood clot, officials say.
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.
She is expected back at her desk on Monday, Mr Reines said.
Mrs Clinton is due to give evidence before a Congressional committee on 10 January in connection with the attack in September on the US consulate in the Libyan city of Benghazi.
The US ambassador to Libya and three American officials were killed in the incident.
Mrs Clinton was appointed secretary of state at the start of Mr Obama's first term, in January 2009.
Her most recent foreign trip was to Dublin earlier this month. (bbc.co.uk)