Secretary of State Hillary ClintonHillary Diane Rodham ClintonPelosi on power in DC: 'You have to seize it' Cuba readies for life without Castro Chelsea Clinton: Pics of Trump getting vaccinated would help him 'claim credit' MORE was hospitalized on Sunday after doctors found a blood clot.

Clinton is receiving treatment at Presbyterian Hospital in New York where doctors will monitor her for the next 48 hours, her spokesman Philippe Reines said in a statement. 

The clot, resulting from a concussion she suffered earlier in December, was found during a follow-up exam on Sunday, according to the State Department.

"Her doctors will continue to assess her condition, including other issues associated with her concussion. They will determine if any further action is required," Reines said.

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Clinton fainted and suffered a concussion earlier in the month when she was suffering from a stomach virus. At the time, the State Department said that she would continue her recovery at home and was being monitored by her physicians.

The illness forced the secretary to cancel a trip to the Middle East and an appearance before Congress.

Clinton was due to testify before Congress on Dec. 20 about the investigation into the September attack on the U.S. Consulate in Benghazi, Libya, which killed four Americans.

Two senior aides to Clinton testified on her behalf, but Republicans, who have been sharply critical of the administration’s handling of security for the Benghazi mission, have said they still expect Clinton testify in person.

Clinton has said she will step down from her post as the nation’s top diplomat, and President Obama has nominated Sen. John KerryJohn KerryMcCarthy hails 'whole-of-government approach' to climate Biden must compel China and Russia to act on climate The Hill's Morning Report - Presented by Tax March - US vaccine effort takes hit with Johnson & Johnson pause MORE (D-Mass.) to succeed her.

— Amie Parnes contributed to this report.

— Updated at 10:03 p.m.