The 25-year-old Lopez has a 6-5 record and a 4.13 ERA and 16 saves over 111 relief appearances during three Minor League seasons with the Padres and Yankees organizations. In 2008, he pitched at three levels within the Padres farm system: Class A Lake Elsinore, Double-A San Antonio and Triple-A Portland, making a combined 58 relief outings.
Lopez was originally signed by the Yankees as a non-drafted free agent in 2002.
Boone, 36, underwent heart surgery last month and is expected to be out the entire season.
Alyson Footer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.