Leach, 28, pitched in 38 games in relief for the Dodgers in 2009, but he regressed in '10 and never reached the Major Leagues, splitting the season between relieving at Triple-A and starting at Double-A. He was 3-2 with a 6.35 ERA at Albuquerque and 7-3 with a 4.57 ERA at Chattanooga.
Leach was a sixth-round Draft pick in 2005 out of Delta State University, missing the 2004 season with Tommy John surgery.
Guerrier was signed last week to a three-year, $12 million contract to bolster the Dodgers' bullpen.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.