President Michael D Higgins will stay in hospital overnight to receive antibiotics.
Áras an Uachtaráin has confirmed that President Higgins travelled to St James Hospital by arrangement to have a localised infection examined.
A spokesperson said the President is in good spirits and will be returning to Áras an Uachtaráin.
President Higgins remains in office until Catherine Connolly's inauguration in Dublin Castle on 11 November.
Last year, President Higgins spent several days in St James Hospital as a precaution to monitor his blood pressure.
At the time, the President thanked the public for the "outpouring" of support he received and expressed his "deep appreciation to all those who have sent messages to him, as well as to the medical staff for their continuing care."
It comes as President Higgins congratulated president-elect Ms Connolly following her election victory.
Ms Connolly received over 63% of the first preference votes and was elected on the first count.
President Higgins added that Ms Connolly will have the full support of his office as she prepares for her inauguration.
In a statement, he said: "I have this evening spoken by telephone with the president-elect, Catherine Connolly. I congratulated the president-elect on her election as the tenth President of Ireland on what is a momentous day for her and her family.
"The president-elect will have the full support of this office as she prepares for her inauguration next month," he added.
