Waldron will serve as the opening pitcher in Wednesday's game against Colorado, Mark Zuckerman of NatsJournal.com reports.
Waldron was claimed off waivers from Toronto on Saturday, and he's now set to make his Nationals debut in the first inning of Wednesday's contest. The 29-year-old righty owns an unsightly 7.54 ERA and 1.62 WHIP through 37 innings in the majors this season and will likely pitch just an inning or two before coming out of the game.