Yankees manager Joe Girardi said that there is swelling in the joint of Posada's thumb, which prompted him to leave the catcher out of the lineup for the second straight day as New York opened a four-game weekend series with the Blue Jays.
Posada took a foul ball off the thumb in Wednesday's 4-2 victory against the Mariners, and Girardi said that it was not an unusual play that would cost him any sizable amount of playing time.
"The concern is if it gets hit again," Girardi said. "It will heal, and I'm not concerned about it healing. But you're in a tough position when it's your left thumb to heal, in a sense.
"If it gets dinged again, then you go right back to where you are. You try to get it as healthy as possible before you send him out there."
Francisco Cervelli made the start for the Yankees in place of Posada, who is batting .267 with 10 home runs and 33 RBIs in 49 games this season.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.