The 34-year-old Fossum last pitched in the majors in 2009 with the New York Mets and spent last season with the Mets' Triple-A team at Buffalo.
Fossum is 40-53 with a 5.45 ERA in nine big league seasons. Selected by Boston in the first round of the 1999 amateur draft, Fossum broke into the majors with the Red Sox in 2001 and pitched for Arizona, Tampa Bay and Detroit before his three-game stint with New York in 2009.
He has made 120 starts in the majors without a complete game and has 237 big league appearances.
Fossum was not invited to major league spring training camp.