"I think any time you start seeing guys nicked up, it's a concern," Girardi said. "We've talked about the importance of giving guys days off, because we have some -- I don't want to insult them, but -- older players on our club. We have to be careful, and we have to be smart about spelling them when they need it."
Posada left Monday's game with tightness in his right calf and was sent to New York-Presbyterian Hospital. The 38-year-old caught the first five innings before Francisco Cervelli replaced him in the sixth.
Girardi said that Posada told him it felt like someone had hit him in the calf during his fourth-inning at-bat against the Orioles' Jeremy Guthrie.
It was immediately unknown if the Yankees would add another catcher before Tuesday's game, but Girardi guessed that Posada would be only an emergency catcher until at least Friday.
Meanwhile, Rivera has been quietly absent since reporting some stiffness in his left side -- technically, his flank -- after first feeling pain in his most recent appearance, on Friday against the White Sox.
Rivera described the discomfort as similar to the stiffness he felt in his right side during last year's postseason, and he said it was "no big deal," having played catch without incident on Monday.
Rivera feels it when he sneezes, for example, but the right-hander believes he would be available to pitch on Tuesday.
"I threw today and I felt good, but I didn't want to push it," Rivera said. "We'll throw off a mound [Tuesday] and see if everything feels good."
Rivera said that had it been later in the season, he would have been on the mound. With a three-run lead against the Orioles at this point in the year, however, Rivera was happy to see Joba Chamberlain retire the side for his second career save.
"Definitely, I would have been pitching -- it's May," Rivera said. "It won't hurt us. It's early. We'll have to take care of it and make sure we're good the rest of the season."