Clinton was admitted to a New York hospital on Sunday after doctors discovered a blood clot related to a concussion she suffered early this month while she was recovering from a stomach infection.
"In the course of a routine follow-up MRI on Sunday, the scan revealed that a right transverse sinus venous thrombosis had formed," said Dr Lisa Bardack from Mt Kisco Medical Group, and Dr Gigi El-Bayoumi, from George Washington University, in a statement.
"This is a clot in the vein that is situated in the space between the brain and the skull behind the right ear," the doctors treating her said a day after she was admitted to the New York-Presbyterian Hospital.
"It did not result in a stroke, or neurological damage.
To help dissolve this clot, her medical team began treating the Secretary with blood thinners. She will be released once the medication dose has been established," doctors said in a statement.
"In all other aspects of her recovery, the Secretary is making excellent progress and we are confident she will make a full recovery.
"She is in good spirits, engaging with her doctors, her family, and her staff," the statement added.