A procedure, called a microdiskectomy, to remove a herniated disk was performed Tuesday by Dr. Robert Watkins at an undisclosed hospital and is expected to require a three-month hospital stay.
The procedure followed a two-year absence to recover from "Tommy John" left elbow reconstruction surgery.
Milton, 33, a State College, Pa., native, went 2-1 with a 3.80 ERA in five starts (23 2/3 innings) this season.
The back injury forced the Dodgers to place him on the 15-day disabled list on June 28.
In 10-plus major league seasons with Minnesota, Philadelphia, Cincinnati and the Dodgers, Milton has an 89-85 career record with a 4.99 ERA.
The Los Angeles Times said the top candidates to be the team's No. 5 starter in Milton's absence are southpaw Eric Stults and right-handers James McDonald, and Jason Schmidt.
Copyright 2009 by United Press International.