The Nationals designated Pilkington for assignment Wednesday.
The transaction frees up a spot on the 40-man roster for waiver claim Tsung-Che Cheng. Pilkington appeared in 34 games for the Nationals last season, posting a 4.45 ERA and 34:17 K:BB over 28.1 innings. The 28-year-old lefty stands a good chance of passing through waivers unclaimed, but if that happens he would have the ability to elect free agency.