The Mets have designated right-handed reliever Brandon Lyon for assignment, according to the team's official Twitter feed.
New York will recall fellow righty Greg Burke to take Lyon's roster spot, the team further tweets.
After a solid 2012 season in which he put up a 3.10 ERA, 9.3 K/9, and 3.0 BB/9 over 61 innings for the Astros and Blue Jays, Lyon signed on with the Mets for 2013.
He is currently sporting a 4.91 ERA in 33 innings thrown, though he was sitting at 3.16 earned per nine before the Nats came into town. Lyon has, however, failed to match last year's strikeout to walk ratio: he has registered 6.3 K/9 against 3.5 BB/9 to date.