The 34-year-old right-hander is 18-18 with two saves and a 4.74 ERA in 238 career games with five major league teams. Grilli went 4-1 with three saves and a 1.93 ERA while pitching for Triple-A Lehigh Valley in the Philadelphia Phillies' organization earlier this year.
Grilli last pitched in the majors with the Texas Rangers in 2009. He missed the entire 2010 season after undergoing right knee surgery. Grilli pitched for Pittsburgh manager Clint Hurdle when the two were with the Colorado Rockies in 2008-09.