The Mets optioned Walker to Triple-A Syracuse on Monday, Anthony DiComo of MLB.com reports.
Walker has been stellar in Triple-A but has yet to translate his success into the majors. He holds a 7.50 ERA and 2.00 WHIP through seven appearances out of the bullpen this season and will now head back to Syracuse in order to return to form. T.J. McFarland was selected from Triple-A in a corresponding move to take Walker's place.