MEXICO CITY — A staffer for Mexican President Enrique Pena Nieto says his thyroid growth is benign.

Pena Nieto will undergo surgery next week to remove the thyroid nodule.

The staffer was not authorized to be quoted by name, but said Thursday the president's operation will only last about an hour and a half, so there is no plan to designate an acting president.

He will have the operation at the Central Military Hospital in Mexico City on July 31.

Mexico's Constitution says nothing about such brief periods of incapacity.

It says Congress can name a substitute within 60 days of the "absolute absence" of a president.

The Interior Secretary would take over as acting president in the interim.