Joe Thatcher (shoulder) will begin a rehab assignment with Single-A Lake Elsinore on Sunday. He'll make just one appearances for Lake Elsinore before moving up to Triple-A Tucson, where he's expected to throw 15 rehab innings. "This will be his spring training," Padres manager Bud Black said. Thatcher had shoulder surgery in early May and has yet to appear for the Pads this season.