Posada underwent testing by a neurology specialist at New York-Presbyterian Hospital during Wednesday's game, telling manager Joe Girardi that he felt "foggy" after taking a foul tip on Tuesday. Those exams came back negative.
The Yankees announced after Wednesday's game that physicians have cleared Posada for competitive play, and he is considered day-to-day.
"I saw him today and asked him how he felt," Girardi said. "He said he didn't sleep a whole lot last night and he had somewhat of a headache, but I heard him laughing in the [players'] lounge. That made me feel better. Jorgie has one of those laughs that carries."
The Yankees are mindful of how head issues have affected other teams. Across town, Mets outfielder Jason Bay has missed a significant portion of the season with a concussion, and the Twins' Justin Morneau has been sidelined with the same malady.
"Any time you start talking about concussions, and we've seen a lot of these last a long time in players, there is concern," Girardi said. "I have contemplated that we might not have him for a little bit here. If that's the case, we've got to deal with it."
Posada's absence on Wednesday was noted because of a situation in which the 39-year-old switch-hitter could have been used in the seventh inning. Instead, backup Francisco Cervelli grounded out, stranding two runners aboard with the Yankees trailing by a run.
The light-hitting Cervelli is hitting .215 with just two RBIs since the All-Star break and batting .252 overall, but he didn't seem fazed by the suggestion that Posada could miss some time.
"If I've got to do it, let's do it," Cervelli said. "I've got to catch and keep the pitching in line."
Still, losing Posada at this point of the season for an extended stretch would figure to be a damaging blow for the Yankees.
"You're talking about a guy that's playoff-tested, World Series-tested, September-tested and down-the-stretch-tested," Girardi said. "He's a switch-hitter in the middle of our lineup. It's an impact."
Cervelli and journeyman Chad Moeller are the other catchers currently on New York's roster.
"We take a lot of pride when guys go down and we have guys to step up and step into big positions," said outfielder Nick Swisher, who hit a walk-off homer with one out in the ninth inning on Wednesday. "Cervy and Chad are really going to have to step it up, and we expect that from them."
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.