The Mets are expected to select Hammer's contract from Triple-A Syracuse on Thursday, Anthony DiComo of MLB.com reports.
Hammer has split time this season between Double-A Binghamton and Triple-A Syracuse, logging a 2.16 ERA, 1.26 WHIP and a 38:21 K:BB across 33.1 combined innings. He will be making his MLB debut whenever he gets into a game.