Palmer, who turns 34 later this month, had similar surgery on his right knee in 2010, but said he never had a problem with the left one and saw no sign that a problem was coming.
"Out of nowhere," he said. "I do believe this is real minor and I'll be back in three to six weeks. God has a reason for everything. I've just got to fight through it."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.