The Nationals recalled Machado from Triple-A Rochester on Sunday.
He'll rejoin the big-league bullpen as a replacement for right-hander Victor Arano (shoulder), who was placed on the 15-day injured list in a corresponding move. Over 43.1 innings with the Nationals on the season, Machado has logged a 4.57 ERA and 1.43 WHIP to go with one win and two holds.