Rainey landed on the 10-day injured list with a right flexor strain Tuesday, Mark Zuckerman of MASNSports.com reports.
The move was made retroactive to Saturday, so Rainey could theoretically rejoin the team Monday for the final week of the season, though that would only be possible if it's a mild strain. His loss will be a blow to the struggling Nationals, as he owns a 2.66 ERA, 0.74 WHIP and 42.7 percent strikeout rate in 20.1 innings this season. Aaron Barrett was recalled in a corresponding move.