SCOTTSDALE, Ariz. -- The satisfaction of breaking Spring Training camp yielded to a sickening feeling among the Giants on Friday when ace left-hander Madison Bumgarner sustained a fracture on the fifth metacarpal of his pitching hand, which he said will sideline him for at least four to six weeks.

The injury, which resulted from a third-inning line drive hit by Kansas City's Whit Merrifield, probably won't idle Bumgarner through the mid-July All-Star break, but he cannot throw a baseball until he undergoes removal of a pin that will be inserted in his hand on Saturday. That must remain in place for close to four weeks to provide stability. After that, Bumgarner will need at least a couple of weeks to rebuild arm strength.

"Obviously, I'm not a doctor or a trainer," Bumgarner said after the Giants' 9-6 loss. "It's just info I'm gathering."

Bumgarner's misfortune alone was stunning enough for a Giants ballclub that pinned much of its hope for 2018 upon him. However, it was paired with the news that right-hander Jeff Samardzija, San Francisco's No. 3 starting pitcher, would miss three to five weeks with a strained right pectoral muscle.

Losing one starter, particularly the ace, is bad enough for any ballclub. Losing two starters for an extended period threatens to blunt the Giants' momentum before the season even begins.

"It's tough, but I can handle it," said Bumgarner, adding that he knew immediately that his hand was fractured. "These guys can handle it. This obviously was not what I was expecting out of my last start. But it happened, and I can deal with it."

Said left-hander Derek Holland , "This is devastating to see something like this happen."

Merrifield said he has been trying to get in contact with Bumgarner since leaving the game in Scottsdale and learning of the fracture late Friday afternoon.

"I feel awful, this coming in his last start of the spring. Obviously there was no intent," Merrifield said. "I just feel terrible. He's my kind of player, my kind of pitcher. He goes out there and grinds and does whatever it takes to win. I loved watching him pitch."

The Giants learned what life was like without Bumgarner last year, when he was sidelined for three months following a dirt-bike mishap during a scheduled off-day in Denver on April 20. Bumgarner sustained bruised ribs and a sprained left shoulder which sidelined him for three months. The Giants sank into last place in the National League West en route to a 64-98 finish, their second-worst record since 1903.

"I think we saw what can happen," Giants manager Bruce Bochy said. "We've got to bow our necks and play our best ball until these guys get back."

The quality of Bumgarner's five previous Cactus League performances made his injury all the more frustrating. He entered Friday with a 2.84 ERA, 27 strikeouts and three walks in 19 innings and a .217 opponents' batting average.

Given the jolting events of the previous 24 hours, the Giants hadn't had time to re-shape their starting rotation. But it's virtually certain that right-hander Johnny Cueto will ascend to the top of the rotation and inherit Bumgarner's Opening Day start Thursday at Los Angeles. Chris Stratton, Holland and Ty Blach will complete the foursome that the Giants will use through most of April.

Rookies Tyler Beede and Andrew Suarez also will be considered for promotion, though with five scheduled off-days in April, the Giants will rarely need a fifth starter at the season's outset.

However, the Giants didn't lose merely pitchers. They lost symbols.

In Bumgarner, the Giants lost their top starter who became a legend with his record-setting durability in the 2014 postseason.

In Samardzija, they lost a workhorse. Only Samardzija and the Nationals' Max Scherzer have eclipsed the 200-inning mark for five consecutive seasons.

"These are two heavyweights that have carried the team," said Holland, who's 69-64 in nine Major League seasons. "'Bummy' today, that sucks. ... It's up to me. I gotta do what I can to help this team and keep everything going in our direction."