Lilly underwent a debridement, which is the removal of dead, damaged or infected tissue, in this case in the meniscus, which is cartilage in the knee joint. The 25-minute procedure was done by Cubs team orthopedic specialist Stephen Gryzlo.
"Everything went very well," Cubs manager Lou Piniella said.
Lilly, the Cubs' only All-Star, was placed on the disabled list on Saturday, retroactive to July 21, because of inflammation in his left shoulder. The team decided to take advantage of the time off and take care of Lilly's knee at the same time.
Lilly (9-7, 3.59 ERA) last pitched July 20 in Philadelphia. He yielded a career-high nine runs over four innings in the start. His knee has bothered him since mid-June, while his shoulder problems didn't pop up until after the start vs. the Phillies.
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.