SAN FRANCISCO -- There are parts of outfielder Dave Roberts' body that belong in a medical museum. Since serving time on the disabled list for the first time in 2001, the litany of setbacks have accumulated.

Giants manager Bruce Bochy alluded to the fact Roberts may have needed some surgery on his left knee when he originally went on the disabled list four days ago.

The diagnosis wasn't good for the 35-year-old Roberts, who went under the knife Saturday morning to clean out cartilage behind his kneecap caused by arthritis. He'll likely miss at least three months and won't be doing anything for 10 weeks.

"We're going to go slow at first," Giants head trainer Dave Groeschner said. "He did have a significant amount of arthritis in there. We'll see how he responds after the first three weeks. We're definitely going to take it a little bit easy at first to make sure these things don't come back."

San Francisco orthopedist Ken Akizuki performed the procedure, which took less than an hour. Roberts will be on crutches for the foreseeable future. If his rehab goes according to plan, Roberts will start a Minor League rehab assignment in two months.

Roberts went on the disabled list for the eighth time in his career. He's been a regular on the DL in seven of the past eight years. A strained right hamstring put him on the shelf three times, while he's also endured left shoulder surgery, a right knee bruise, a strained left groin and last year's left elbow surgery.

"We want this thing to clear up," Bochy said.

Roberts was hitting .118 (2-for-17) this season in six games. His next hit will be career No. 700.

Fred Lewis (and his 56 career hits through Friday) will take his place in the lineup.