Nationals manager Dave Martinez said Monday that Kieboom hasn't played in any of Triple-A Rochester's last four games due to right lat soreness, Jesse Dougherty of The Washington Post reports.
Martinez revealed that Kieboom was sent in for an MRI, but the organization has yet to receive the results of his medical tests. Rochester has yet to place Kieboom on the 7-day injured list, so he's presumably being viewed as day-to-day.