"We tried to pinpoint something, but it was just a little bit of stiffness that I tried to just kind of count off and not give it too much," Kelley said. "I kept pushing through it and it got a little bit tighter."
Kelley said that he has never had back problems before, but he started to notice some stiffness during the Yankees' series against the Angels earlier this week. He is 1-2 with a 3.52 ERA in 16 relief appearances for New York this season.
Bryan Hoch is a reporter for MLB.com. Follow him on Twitter @bryanhoch and read his MLBlog, Bombers Beat. This story was not subject to the approval of Major League Baseball or its clubs.