The 36-year-old, coming off a season in which he served two stints on the disabled list, has not pitched since mid-August because of right elbow tendinitis and a partial tear of his flexor tendon.
A veteran of 13 major league seasons, the right-hander spent the last seven years with the St. Louis Cardinals. Injuries limited him to 42 appearances and 12 saves in 2008, his lowest total since converting to closer in 1999.
A right hand laceration also sidelined him for 26 games from May 15-June 13, and the two-time All-Star had surgery in September to repair the problem with his flexor tendon.
Isringhausen's 293 saves are the sixth highest among active players. He is the Cardinals' career leader with 217.
In addition to being an AL All-Star in 2000 and NL All-Star in 2005, Isringhausen pitched in five postseasons for Oakland and St. Louis, including the 2004 World Series with the Cardinals. He made his major league debut with the New York Mets in 1995.