But the All-Star outfielder also said he expects to be ready by Opening Day of 2013.
"I wish it just would have been a cleanup and taken six weeks," said Kemp, who begins his rehabilitation Wednesday in Arizona. "They actually had to go repair some things. Now, I think it's going to be closer to January before I'm getting to hit and do a lot of other things."
Kemp, the runner-up to Ryan Braun for the 2011 National League MVP, injured the shoulder banging into a wall in Colorado on Aug. 28. He batted .214 with 15 RBIs in 28 games after hurting his shoulder.
"I already asked the doctor, 'If I played on it, could I damage it any more than it's already damaged?' and he said 'No,' so I kept playing on it," Kemp said. "They went in and were surprised I was still playing on it. They said it was worse than they thought. They sewed it back together, and I'll start my rehab."
In the 60-minute procedure on Oct. 5, team orthopedist Neal ElAttrache repaired a partially torn labrum and rotator cuff damage. Kemp said Wednesday the shoulder is still sore.
Both Kemp and Dodgers left fielder Carl Crawford will enter the 2013 season coming off surgery. Crawford had Tommy John surgery on his left elbow in August, and the Dodgers are hopeful he can return some time in April.
If Kemp isn't ready to begin the season, the Dodgers could use Tony Gwynn Jr. in center field. They also have Cuban defector Yasiel Puig, who finished last season at Class A Rancho Cucamonga and likely won't be ready by Opening Day.
Kemp also missed 51 games last season with hamstring injuries.
"I've got to sit here and not do very much right now," Kemp said. "All I can do is watch the Giants and Detroit play on TV. I'm definitely getting the itch to get back out there and get myself ready for the season."