SAN FRANCISCO -- Left fielder Dave Roberts' possible extended absence from the Giants' lineup with an injured left knee will create more playing time for Fred Lewis, manager Bruce Bochy affirmed Wednesday.

Bochy explained that since the Giants -- as do all Major League teams -- face a preponderance of right-handed starters, the left-handed-batting Lewis will play more than Rajai Davis, a right-handed hitter.

"I said a few days ago that Fred's playing time would definitely increase, and it is now," Bochy said.

Bochy also said that Lewis, Eugenio Velez and Davis, when he's starting, will share the leadoff duties that belonged to Roberts. Velez, who's likely to bat first most frequently, hit leadoff for the second time this season in Wednesday night's series finale against the San Diego Padres. Davis has led off once so far.

Meanwhile, Roberts sounded resigned to undergoing surgery, which could sideline him for more than the standard 4-6 weeks. Roberts has a torn meniscus in his knee and a case of chondromalacia, commonly known as "runner's knee" -- a degenerative condition of the cartilage surface in the back of the kneecap. That has caused Roberts' knee to swell regularly since Spring Training.

Roberts said that he expects to receive a second opinion Thursday from Dr. Lewis Yocum, the Los Angeles Angels team physician. On Wednesday, Roberts consulted with Giants team orthopedist Dr. Ken Akizuki, who advised the 35-year-old that surgery wouldn't be a simple procedure.

"For me to kind of miss out on the first couple of months is very disheartening," said Roberts, who missed a month last year after undergoing surgery to remove bone spurs from his left elbow. "But hopefully things turn a little bit for us and the last few months of the season matter and I can be a part of it."