Mercer (calf) was reinstated from the 10-day injured list Monday, Mark Zuckerman of MASNSports.com reports.
Mercer landed on the injured list with a left calf strain July 24, but he began a rehab assignment at Double-A Harrisburg last week. He went 3-for-9 with a run, two walks and three strikeouts across three rehab games and will rejoin the Nationals as utility depth after Adrian Sanchez was designated for assignment.