The Mets needed to make a move after calling up second baseman Dilson Herrera.
Leathersich made his first two major league apperances this week after being called up Tuesday. He pitched a third of an inning at Miami Wendesday and two-thirds of an inning Thursday against the Nationals. He allowed two hits, struck out one, and threw 13 of 15 pitches for strikes.
Leathersich, 24, struck out an average of 15.3 batters per nine innings in the minors since being drafted by the Mets in 2011.
In seven relief appearances with Triple-A Las Vegas this season, Leathersich has a 2.57 ERA and walked just two batters, while striking out 13 in seven innings. He walked 36 batters in 37 innings with Triple-A Las Vegas the two previous seasons.