Rivera sidelined by stiffness in left side

Closer Mariano Rivera was unavailable for the New York Yankees game against the Baltimore Orioles on Monday due to stiffness in his left side.

Apparently, Rivera has not been available since Friday night, when he closed out the 6-4 win over the Chicago White Sox but felt the stiffness.

"It didn't affect me at all," Rivera said. "I finished pitching the game, but I felt it, you know? I can't even describe it. I didn't feel any pop or pull or anything like that. But it's like, when I sneeze, I feel it."

Rivera played catch Monday and will try to throw off a mound Tuesday. He is day to day.

"I'm not worried at all," he said. "Like I said, I threw today and it felt good but I didn't want to push it."

The injuries continued to pile up for the Yankees after catcher Jorge Posada left Monday's 4-1 win early with a mild right calf strain. Like Rivera, he is day to day.

"I think any time you start seeing guys get a little bit nicked up it's a concern," Yankees manager Joe Girardi said.

Information from ESPNNewYork.com's Wallace Matthews and The Associated Press contributed to this report.