Carter Kieboom, a first-round draft pick and the expected starting third baseman for the Washington Nationals, was sent to the minor leagues on Saturday.

Drafted in 2016, Kieboom has struggled at the plate in limited opportunities in the majors, batting .181 in 44 games over two seasons with Washington. Kieboom and Starlin Castro had been getting time at third in preseason camp.

Also optioned to Triple-A Rochester were infielder Luis Garcia, left-handed pitcher Sam Clay, right-handed pitcher Kyle McGowin and outfielder Yadiel Hernandez.

Surprising additions to the team's major league roster were INF Jordy Mercer and INF/OF Hernan Perez. Mercer has a split contract: $1,000,000 while he's in the majors and $150,000 in the minors, plus $50,000 each for 100, 150, 200 and 250 plate appearances, and $100,000 each for 300 and 400 plate appearances.

Re-assigned to minor league camp were RHP Aaron Barrett, RHP Paolo Espino, RHP Javy Guerra, RHP Todd Peterson, catcher Welington Castillo, C Brandon Snyder, C Blake Swihart, INF Adrían Sanchez, OF Gerardo Parra and OF Carlos Tocci.

The Nationals also released Yasmany Tomas and T.J. McFarland from their minor league contracts, and first baseman Jake Noll was designated for assignment to clear space on the 40-man roster.