Bay was set to hit fifth Thursday night against Houston. He had been out since spring training because of a strained left rib cage.
The Mets have the worst record in baseball at 5-13 and are hitting just .238.
To make room for Bay, the Mets placed Bobby Parnell on the 15-day DL because of numbness in his right middle finger. Team doctors suspect a blood clot is causing the problem and Parnell will be treated with aspirin.
Bay has not played since July 25 because of a concussion. Last season he hit .259 with six homers and 47 RBIs.