Cristina Fernandez de Kirchner, 60, was earlier ordered to rest for a month after doctors discovered the subdural hematoma.
The subdural hematoma was diagnosed as she was undergoing tests for another condition on Saturday.
This means Cristina Fernandez de Kirchner will have to suspend campaigning for congressional elections.
The break from campaigning is considered awkward for the president as some opinion polls have suggested the government could lose control of Congress in the poll on October 27.
Medical experts say recovering from this type of surgery is a long process, and her lay-off is now likely to be longer than a month.
The president’s spokesman, Alfredo Scoccimarro, had issued a statement on Sunday saying her doctors had carried out a brain scan in August after a previously undisclosed trauma – thought to be caused by a fall.
They found nothing untoward, but on Saturday, she went to hospital for checks for an irregular heartbeat and also complained of headaches.
A further scan revealed the subdural hematoma – bleeding between the brain and the skull.
The hospital treating her said on Monday she had experienced a slight loss of muscular strength in her left arm the day before.
Doctors said she needed surgery to drain the subdural hematoma.
President Cristina Fernandez de Kirchner was first elected in 2007 and then returned to power by a comfortable majority in 2011.
Cristina Fernandez de Kirchner’s husband, former President Nestor Kirchner, died after a heart attack in 2010.
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