Poulin will be the Nationals' opening pitcher in Monday's game versus the Guardians, Spencer Nusbaum of The Athletic reports.
It will be the sixth opener assignment this season for Poulin, who has permitted only one run with a 5:1 K:BB over 6.1 innings in the first five of those outings. Zack Littell is in line for bulk relief duty for the Nationals on Monday.