SAN FRANCISCO -- Giants left fielder Dave Roberts, who admitted that he might need surgery to repair his injured left knee, went on the 15-day disabled list Tuesday.

"I don't think we're 100 percent committed to it, but it's a viable option at this point," Roberts said.

The Giants officially said before their 3-2, 11-inning victory over San Diego that Roberts had inflammation in his left knee. But Roberts said after the game that he had a torn meniscus in his knee and "stuff under my kneecap" that was causing frequent swelling.

Roberts, 35, had endured soreness in the knee since Spring Training. But he was the Giants' Opening Day left fielder and started five of the first seven games, hitting .118 (2-for-17) with one RBI.

There had been no overt hints that Roberts would go on the disabled list, although manager Bruce Bochy recently referred to the need to rest him periodically to relieve stress on his knee.

Roberts revealed that he had received "multiple cortisone shots" and anti-inflammatory treatments, besides periodic rests, in efforts to improve his knee. He indicated that he might seek a second medical opinion before resorting to surgery.

"We want this thing to clear up," Bochy said. "It's early [in the season] and he was getting some swelling on that knee after every game. His game is his legs and he wasn't able to use them like he normally does."

Roberts became the fifth Giant to go on the disabled list, joining shortstop Omar Vizquel, left-hander Noah Lowry, right-hander Vinnie Chulk and infielder Kevin Frandsen.

To replace Roberts on the active roster, the Giants recalled outfielder Clay Timpner from Triple-A Fresno. He made his Major League debut Tuesday against the Padres, playing the final two innings in left field and striking out in his lone at-bat.

Timpner, 24, is beginning his fifth professional season with the Giants, who selected him in the fourth round of the 2004 First-Year Player Draft. He hit .083 in Spring Training (1-for-12) but was batting .250 (5-for-20) with six RBIs in four games for Fresno while playing center field. Last year with Fresno, Timpner hit a career-high .301 with six homers and 39 RBIs in 109 games.