Bay landed on the disabled list April 24 with a fractured rib on his left side, which he suffered on an attempted catch of Gregor Blanco's fly ball the previous day, in Game 2 of a doubleheader against the San Francisco Giants.
Bay served as a designated hitter the past two days for Class A St. Lucie. He had been due to play the outfield for the Florida State League club on Monday night to complete a rehab assignment.
With rookie Kirk Nieuwenhuis' success in Bay's absence, the Mets have a logjam in the outfield.
Manager Terry Collins acknowledged it will be a challenge finding playing time for five outfielders.
Andres Torres, Bay and Nieuwenhuis likely will form some type of rotation between left and center field. Lucas Duda will remain the primary right fielder, with Scott Hairston chipping away at the playing time by starting against left-handed pitching.
Collins will get a brief reprieve beginning next weekend. The Mets will play six straight games in American League ballparks starting Friday, against the Yankees and then the Tampa Bay Rays.
Bay can be used as the designated hitter during interleague play, Collins said.
The Mets also are expected to get shortstop Ruben Tejada back for Friday's series opener at Yankee Stadium. Tejada, on the DL with a right quadriceps strain, is due to begin a rehab assignment Monday with Triple-A Buffalo.
Right-hander Chris Young will return from May 16, 2011 surgery to repair a torn anterior capsule in his right shoulder for Tuesday's start in Washington.
Fellow right-hander Miguel Batista (back/oblique strain) also is scheduled to be activated from the DL that day.