Armenteros was designated for assignment Tuesday, Jessica Camerato of MLB.com reports.
Armenteros recorded a respectable 4.00 ERA in his 18-inning debut back in 2019 but has failed to crack the active roster since then. He missed last season due to elbow issues and has struggled to a 5.83 ERA in seven starts for Triple-A Rochester this season. The move clears space on the 40-man roster for the Nationals to select Justin Miller's contract.