Kotsay's surgery removed a displaced disc fragment, and the timetable for his return is uncertain.
However, the Red Sox don't expect Kotsay to miss much time during the regular season. The procedure was performed by Dr. Robert Watkins.
The injury to Kotsay further explains the addition of free agent Brad Wilkerson, who agreed to terms on a Minor League deal with the Red Sox on Tuesday.
Like Kotsay, Wilkerson is a left-handed hitter and thrower who plays first base and the outfield.
Kotsay is Boston's primary backup to Kevin Youkilis at first base and is the fifth outfielder behind Jason Bay, Jacoby Ellsbury, J.D. Drew and Rocco Baldelli. Wilkerson should slide into that same role while Kotsay is out.
Back problems are nothing new to Kotsay. While with the Athletics, he underwent surgery in Spring Training of 2007, opened the season on the disabled list and had to end his season after just 56 games with more discomfort.
It was also the back that kept Kotsay out of action periodically during the late stages of the 2006 season.
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.