"I don't think we know how serious it is yet," general manager Sandy Alderson said. "We may not know for at least a few days."
Alderson indicated that Bay's "more obvious symptoms" still have not dissipated since the outfielder tumbled into Citi Field's left-field wall on Friday evening, hitting his head against the padding. Bay, who was batting .187 with four home runs in 22 games prior to his injury, missed the final two-plus months of the 2010 season with a concussion. He also sat out six weeks earlier this year with a fractured left rib.
"In this case, I think you've got to let things settle down a little bit before you make an evaluation about when somebody's going to come back," Alderson said. "The thing we don't want to do right now is put any pressure on him to feel as if he's got to come back right away. That's not the case. He may be out quite a while."