Kieboom was sent to Washington's alternate camp site Wednesday, Mark Zuckerman of MASNSports.com reports.
Kieboom has struggled across 14 appearances this month, going just 6-for-41 with zero extra-base hits and 17 strikeouts. There's a chance the 22-year-old rejoins the big club down the stretch, but for now Asdrubal Cabrera (foot) should handle the majority of the playing time at third base.