Gallo is out of the lineup for Monday's game against the Mets, Mark Zuckerman of MASNSports.com reports.
After starting in each of the Nationals' previous four games, the lefty-hitting Gallo will head to the bench while Washington takes on southpaw Sean Manaea in the series opener at Citi Field. Juan Yepez will enter the lineup in Gallo's stead, occupying first base while batting third.