Posada did indeed enter the game as a pinch-hitter, lining out with runners on the corners and one out in the 13th inning.
Posada said that he felt "foggy" after being clipped in the mask by a couple of foul tips during Tuesday's game against the Orioles at Yankee Stadium, and he was sent to a New York hospital on Wednesday for tests after he reported for a matinee game with a persistent headache.
"I felt weird," Posada said. "I didn't sleep a whole lot on Tuesday night for the Wednesday day game. Other than that, I didn't experience anything different than a normal headache."
The Yankees sent word on Wednesday that Posada was cleared for competitive play by a neurology specialist at New York-Presbyterian Hospital, but Posada said that he was told by head athletic trainer Gene Monahan that the catcher had likely suffered a slight concussion.
Posada believes that he has suffered three previous concussions, the last of which came in September 2007 in a home-plate collision with Eric Hinske, then playing for the Red Sox.
"I've had them before," Posada said. "It's not like I haven't experienced them before. You get the headaches, you get a little foggy and stuff, but I don't think I felt like that this time. I'm not concerned."
Posada said he felt fine during the Yankees' flight to Texas and wanted to be in the starting lineup on Friday, but Yankees manager Joe Girardi is taking the cautious route, mindful of how concussions have affected Major Leaguers like the Mets' Jason Bay and the Twins' Justin Morneau this year.
"He's available for us today as a pinch-hitter," Girardi said before Friday's game. "Our fear is if he takes another foul tip. You've seen what has happened to some of these guys who have recently gotten concussions, how long it has taken to come back."
Posada could be available to catch on Sunday and will not make any changes to his equipment behind the plate.
"It all depends where they hit you," Posada said. "If they hit you in the right spot, obviously you're going to feel it. It's part of being back there. You're going to get hit, so this is serious stuff."