Mesoraco said he felt something while swinging in the cage a couple of days ago.
"It was just real minor and I just took a second," Mesoraco said. "I kept trying to swing and kept going and it didn't bother me at all. I came in and sat down and cooled down and went back out. I could just tell that it wasn't quite right. So I kind of shut it down before I did anything to really aggravate it."
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, and follow him on Twitter @m_sheldon. This story was not subject to the approval of Major League Baseball or its clubs.