The San Francisco Giants are suddenly without their best hitter.

Pablo Sandoval has a broken hamate bone in his left hand that will require surgery, and the free-swinging slugger is expected to miss four to six weeks — the same injury he had last year on the other hand.

"You just don't replace a bat like Pablo. This guy was on the All-Star team last year. There are very few guys in major league baseball who can do some things he can do with the bat," manager Bruce Bochy said. "Tough news for us with Pablo. I feel for him, particularly with the way he's been playing and swinging the bat. It's a tough loss, four to six weeks, but it's right thing to do to get this thing taken care of. We'll have to move forward and try to maintain where we're at, and hopefully better, until he gets back. We've just got to keep them believing."

Conor Gillaspie was recalled from Triple-A Fresno to start at third base Thursday in the series finale with the Miami Marlins in place of Sandoval, placed on the 15-day disabled list. The 2010 World Series champions missed the playoffs last year in an injury-plagued season, and this is another tough blow when they hope to contend with the surprising Los Angeles Dodgers and defending division champion Arizona Diamondbacks.

The switch-hitter broke his right hamate bone in late April last year and had surgery. It happened again to the other hand in recent days and he aggravated it swinging left-handed in Wednesday's 3-2, 10-inning loss to the Marlins and had to leave the game in the sixth inning. An X-ray Tuesday did not reveal the break, but Sandoval then underwent an MRI exam and CT scan that showed the fracture. He will undergo surgery Friday at Stanford, performed by Dr. Tim McAdams.

"He doesn't remember doing it on one swing," Giants athletic trainer Dave Groeschner said. "He was hitting right-handed Sunday and the off day Monday, then Tuesday afterward he said it was sore. X-rays are tough on that area. It's not a good way to view it."

The Giants' top hitter and 2011 All-Star needed the full six weeks last year for his throwing hand to recover. The 25-year-old Sandoval is batting .316 with five home runs and 15 RBIs, and he opened the season with a 20-game hitting streak — longest in franchise history to open a year.

"We joked about that earlier, as soon as you're born take out the hamate bone, appendix, wisdom teeth, just get it done early," Bochy said.

The Giants expect Aubrey Huff to come off the disabled list Monday after his battle with anxiety disorder. Huff has been working out and taking batting practice, while giving Bochy indications he is ready both physically and mentally to get back on the field.

"Huff is available to come on Monday, which would be a shot in the arm for us," Bochy said. "But until then we've got to really pick it up and do a better job with runners in scoring position. ... (Huff) has been working hard getting ready for that day. He really believes that he's going to be ready for that day that he can come off. He'll give us some experience in the heart of the order, which I believe we really need."

Gillaspie batted in the No. 2 hole and Bochy moved regular leadoff man Angel Pagan to fifth to give the struggling Giants offense a reliable bat in the middle of the order.

"Conor has been swinging the ball well down in Fresno," Bochy said.