Lucas Duda started in leftfield in Bay's place. Duda, who hit .118 with the Mets earlier this season, was hitting .257 with three home runs and nine RBIs in 21 games for Triple-A Buffalo. Duda went 0-for-2 -- two strikeouts looking -- before being removed for a pinch hitter in the fifth inning.
Manager Terry Collins said he thought Bay could be back by Thursday.
General manager Sandy Alderson said top prospect Jenrry Mejia might not get a second opinion on his elbow until next week because of scheduling issues. Mejia, 21, has been diagnosed with a complete tear of his medial collateral ligament and likely needs Tommy John surgery with a recovery timetable of a year or more.
"Anytime you lose a prospect like that, it hurts," Alderson said. "Given the fact that he was close. He was somebody that we expected to see late this year, certainly next year. This throws that timetable off completely. At the same time, if it was going to go, maybe it's better it goes now and not three years from now."
Alderson said Johan Santana continues to be on schedule in his rehab from shoulder surgery, meaning a midseason return is still possible.
"Back in spring training, we talked about the three phases," he said. "I think at this point, we're at the end of the second phase, which was return to throwing. Within the next two weeks, hopefully, we'll get to that final stage, which is return to pitching."
Alderson said he is hopeful Angel Pagan (oblique) will return from the DL Saturday. Pagan went 1-for-5 in an extended spring training game and played nine innings in center.
Bobby Parnell (finger numbness) has begun to throw, but has to be cleared by a cardiologist before he can begin pitching in rehab games, Alderson said.