The team said the 2007 all-star underwent an MRI exam Friday, which confirmed the injury. Later, he was examined by surgeon Dr. Lewis Yocum.
"I'm going to do everything I can to get back as soon as I can," Lackey said on the Angels' Web site. "I'll be a little bit cautious."
Last season, the 29-year-old right-hander went 19-9 with an American League-leading 3.01 ERA in 33 starts.
He was the Angels' 2007 Opening Day starter and the all-star selection was the first of his six-year career.