Crowe will serve as the 29th man for Tuesday's doubleheader against the Phillies, Jesse Dougherty of The Washington Post reports.
Crowe has spent three separate stints on the Nationals' roster this season. The latest lasted just one day, as he joined the team to start the nightcap of Friday's doubleheader against the Marlins before being optioned the following day. He threw just 2.1 innings in that game, so he should be available for multiple innings if needed out of the bullpen Tuesday.