"He's still having some of the same symptoms," manager Jerry Manuel said. "I'm hopeful that here in the next couple of days, that he just wakes up and doesn't have those symptoms."
Though Bay originally suffered the concussion crashing into Dodger Stadium's outfield wall last Friday, he played Saturday and Sunday and did not begin to feel symptoms until boarding the team plane back to New York on Sunday evening.
After Bay complained of continued headaches during an examination Friday by the Mets' medical staff, the club placed him on the disabled list retroactive to July 26, recalling outfielder Jesus Feliciano from Triple-A Buffalo.
In Bay's absence, Angel Pagan will receive the bulk of starts in left field, with Jeff Francoeur starting regularly in right. Feliciano, who hit .291 in 21 games with the Mets earlier this season, will serve as the team's fourth outfielder.
"We have some depth there," Manuel said.
The Mets have been cautious with head injuries since Ryan Church missed approximately half the 2008 season with post-concussion syndrome. Most notably, the organization forced David Wright to go on the disabled list last season after Matt Cain of the Giants hit him in the head with a fastball.
Bay, who was hitting .259 with six home runs before his injury, will be eligible to come off the disabled list on Aug. 10 if his symptoms allow.
Anthony DiComo is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.