The Mets designated Grey for assignment Thursday.
Grey ceded his spot on the 40-man roster to infielder Deven Marrero, whose contract was selected from Triple-A Syracuse in a corresponding move. The Mets previously called up Grey from Triple-A on Aug. 22, only for him to get demoted five days later without making an appearance out of the big-league bullpen. The 28-year-old righty has been serving as a starter for Syracuse this season, logging a 5.52 ERA over 93 innings.