General manager Mike Rizzo said the Nats will decide after today who will be sent down in order to get the roster back to 25.
Marrero last appeared with the Nationals in 2011, when he hit .248 with 10 RBIs in 31 games. In November of that year, he underwent surgery to repair a torn left hamstring sustained while playing in the Dominican Winter League. Since then, he's been working his way back to the majors, playing at five different levels of the Nats' minor leagues since 2012.
This season at Syracuse, he's batting .304 with 10 homers and 44 RBIs in 55 games.