The Baltimore Sun cited multiple sources saying the issue was Balfour's surgically repaired right shoulder. But Balfour and his representatives insist the closer is healthy. Balfour told The San Francisco Chronicle that he's "100 percent fine."
ESPN.com's Jim Bowden has reported the Rays have interest in Balfour, who was an All-Star last season.
Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak. This story was not subject to the approval of Major League Baseball or its clubs.