SAN FRANCISCO -- The offense-starved Giants were forced to scrape for morsels of optimism Thursday as third baseman Pablo Sandoval, their top run producer, went on the 15-day disabled list with a fractured left hamate bone.

Conor Gillaspie was recalled from Triple-A Fresno to replace Sandoval, who's estimated to be sidelined from four to six weeks.

Of course, as Giants manager Bruce Bochy said, "You just don't replace a guy like Pablo. The guy was on the All-Star team last year. There are few guys in Major League Baseball who can do things he can do with the bat."

There's little doubt that the Giants will miss Sandoval, who had started each of San Francisco's previous 24 games while amassing a team-high five homers and 15 RBIs to complement a .316 batting average. For the Giants, who have struggled mightily to hit with runners in scoring position, Sandoval was a much-needed presence in the batting order's third spot.

"We'll have to maintain where we are and hopefully get better until he gets back," Bochy said.

Sandoval missed approximately 6 1/2 weeks last year when he broke his right hamate bone. But the Giants cited reasons why he could return sooner this time. Sandoval hurt his throwing hand last year, so he had to be more careful in his recovery. Also, the switch-hitting Sandoval was injured last season while batting left-handed, the side he employs predominantly. He sustained his latest fracture hitting right-handed last Sunday against San Diego, prompting the notion that he could return to action and avoid batting from that side until he's more fully healed.

"So there's hope for some optimism," Giants head athletic trainer Dave Groeschner said. "But it is four to six weeks."

Sandoval, 25, will undergo surgery Friday in Palo Alto to have the bone removed. Dr. Tim McAdams will perform the procedure.

"I guess the good news is both [hamate bones] will be gone tomorrow and he can't do it again," Groeschner said with grim humor.

Sandoval homered Sunday when he initially felt discomfort. Tuesday, following Monday's scheduled off-day, he homered and doubled. X-rays taken of his hand Tuesday revealed no fracture, but as Groeschner explained, "X-rays are tough in that area. It's not a good way to view it."

Sandoval underwent an MRI on Wednesday that confirmed the injury, after he left that night's game following a sixth-inning groundout to second base. In that plate appearance against Miami right-hander Carlos Zambrano, said Groeschner, Sandoval hit an outside sinker off the end of his bat.

"It kind of shocked him," Groeschner said.

Gillaspie, 24, will receive the first opportunity to fill the void Sandoval left. A sandwich pick immediately following the first round in the 2008 First-Year Player Draft, Gillaspie was hitting .362 with three home runs and 13 RBIs in 23 games with Fresno. He also compiled a .417 on-base percentage and a .521 slugging percentage.

Bochy immediately installed Gillaspie in Thursday's lineup against Miami, and he went 1-for-3.

"Right now I'm hoping Conor takes it and runs with it," Bochy said before the game. "I'd say he's looking at most of the playing time."

Gillaspie's ready for the responsibility.

"I think everybody knows I can't replace the guy," Gillaspie said, referring to Sandoval. "That's reality. There are very few people who can replace a guy like that. While he's out, I'm going to do the best job I can offensively and defensively."

Gillaspie made a couple of smooth defensive plays Thursday, proving that he heeded the mandate to sharpen his overall game.

"I've worked hard over the last few years to improve on some things I didn't do very well," he said. "Just to get the opportunity, even if it's going in for a guy like [Sandoval], I'm happy to do it. ... Obviously, defensively was where I've struggled. That's where I made the biggest strides."

Gillaspie provided a late-season highlight last Sept. 27 when he hustled out an inside-the-park home run against Colorado. He realizes that he'll have to continue to hustle in this manner.

"I'm not that big of a guy. I don't hit the ball like Pablo does, obviously," said Gillaspie, who's listed as 6 feet and 186 pounds. "But you have to understand your strengths and weaknesses. I probably can't launch a home run too often out of here. But I feel like I have a pretty decent idea of how to get the job done and contribute in some way."

Should Bochy wish to seek alternatives at third base, he'll consider infielders Joaquin Arias, Emmanuel Burriss and Ryan Theriot, who have a smattering of experience at the position. Bochy said that Brett Pill, who has tried to make himself handy at every position, is not an everyday option.

Bochy expressed hope that first baseman Aubrey Huff, who's recovering from an anxiety disorder, can bolster the offense when he leaves the disabled list. That could happen as early as Monday.

"That will be a shot in the arm for us," Bochy said. "He'll give us some experience in the heart of the order, which I believe we really need."

Bochy also expects the rest of the Giants to motivate themselves to upgrade their performance to help compensate for Sandoval's absence. In fact, San Francisco posted a 25-16 record and moved into first place in the National League West while Sandoval was sidelined last year.

"Hopefully some of these guys are going to look at this as a great chance for them to show what they can do and go out and shine," Bochy said.