The Nationals placed Herz (elbow) on the 60-day injured list Wednesday, Mark Zuckerman of MASNSports.com reports.
The move clears a spot on Washington's 40-man roster for Miles Mikolas, who signed a one-year deal with the club Wednesday. It's unclear how close Herz is to beginning a throwing program after undergoing Tommy John surgery last April, but he's likely to be sidelined for at least most of the season's first half.