"He did something we didn't know about, about a month before Spring Training, just doing his workout," Reds manager Bryan Price said. "It's a little bit of a strain. It's not causing any problem with his bullpens, with his lifting or any of his throwing stuff. He was out playing long toss before his last bullpen and he felt it a little bit.
"We've just been really cautious with it. That's one of those situations where if it gets worse, you're looking at a real setback. If we skip him for a start, we're probably looking at a non-issue in another 5-to-7 days."
Leake, 26, is coming off of his best season. He was 14-7 with a 3.37 ERA and set career highs in wins, innings pitched (192 1/3) and starts (31).
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.