Bumgarner broke a bone in his pitching hand Friday when it was hit by a line drive off the bat of Kansas City's Whit Merrifield during a spring training game.
The Giants said X-rays showed the 28-year-old fractured the fifth metacarpal on the outside of his left hand. Bumgarner said the timeline for recovery is four to six weeks and he will have a pin inserted into his pinkie Saturday.
"It's tough. But I can handle it," Bumgarner said. "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."
Bumgarner, the 2014 World Series MVP, missed nearly three months with a shoulder injury last season after a dirt bike accident on April 20 during an off day in Colorado.
His latest setback is a huge blow to the Giants as they try to rebound from a surprising last-place finish in the NL West with 98 losses.
"It's just a downer. This was a short day. I feel for him," manager Bruce Bochy said. "Obviously, we know what he means to us, but where he was, how well he's thrown the ball all spring. Unfortunately, you've got to deal with these things. But this one certainly was a downer today because we were all getting ready to go to San Francisco and now we've got to make some adjustments."
After six straight seasons with double-digit wins, more than 200 innings and 30-plus starts, Bumgarner went 4-9 with a 3.32 ERA in 17 starts last season and threw just 111 innings.
Bochy wasn't ready to say whether right-hander Johnny Cueto would move into the No. 1 spot and pitch Thursday's opener at the NL champion Los Angeles Dodgers. Jeff Samardzija has a strained pectoral muscle that will shut him down for at least a week and likely force him to start the season on the disabled list.
"This is horrible news for us," Bochy said. "There's nothing else we can do now except push on."
ELSEWHERE AROUND THE GRAPEFRUIT AND CACTUS LEAGUES
DODGERS 10, ROYALS (SS) 0
Clayton Kershaw stretched his scoreless streak to 21 1/3 innings with 6 2/3 innings in his final tuneup for Thursday's opener against San Francisco. He allowed a leadoff single to Jon Jay and no other hits. He struck out four and walked none in his first appearance since turning 30 on Monday. Ricky Nolasco , who signed with Kansas City on March 7, allowed eight runs, five hits and two walks over 2 2/3 innings in his first start.
RED SOX 5, YANKEES 0
Aaron Judge hit leadoff for the first time in his professional career and went 1 for 4. Masahiro Tanaka gave up one run and five hits in 5 2/3 innings. Boston's Sam Travis hit his sixth home run and Ivan De Jesus Jr. had three hits, including a home run.
CARDINALS 5, METS 1
Michael Conforto went 1 for 4 as a designated hitter in his first big league game action since surgery Sept. 6 to repair a tear in the posterior capsule in his left shoulder.
PHILLIES 8, PIRATES 2
Maikel Franco hit a two-run homer and a grand slam after entering with a .167 average in 48 at-bats. Aaron Nola allowed four hits in his last outing before his first opening-day start, at Cincinnati.
ORIOLES 6, RAYS (SS) 1
Baltimore opening-day starter Dylan Bundy yielded one run and five hits in five innings, and Chris Davis and Trey Mancini hit two-run homers. Kean Wong, a brother of Cardinals second baseman Kolten Wong , had a pair of hits for the Rays.
RAYS (SS) 6, BLUE JAYS 5
TIGERS 11, BRAVES 3
James McCann doubled twice and drove in five runs. Detroit's Norris gave up three runs — two earned — three hits and four walks in five innings. Anibal Sanchez made his second start for Atlanta, allowing three runs and seven hits in five innings. Freddie Freeman hit his second homer.
ASTROS (SS) 2, TWINS 2
Ryan LaMarre's double leading off the ninth inning was the first hit for Minnesota and Tanner English followed his first homer. J.D. Davis hit a pair of solo homers, raising his total to five.
ROCKIES 8, REDS 2
Homer Bailey , picked to start the Reds ' opener, allowed consecutive homers in the fourth to Nolan Arenado and Carlos Gonzalez . Bailey, limited to 26 starts over the past three seasons because of injuries to his forearm and elbow, gave up three runs and eight hits in five innings.
ATHLETICS 4, ANGELS 2
Albert Pujols hit his first spring training homer for Los Angeles. Jake Smolinski finished a single shy of hitting for the cycle for Oakland.
CUBS 4, BREWERS 3
Ian Happ hit his sixth homer. Tyler Chatwood allowed two runs, six hits and three walks in 5 2/3 innings and also hit an RBI double.
MARINERS 5, WHITE SOX 5,
James Shields struck out three in three shutout innings. Dan Vogelbach hit his sixth homer, Kirk Nieuwenhuis hit a two-run homer and pinch-hitter Craig Dedelow had a tying three-run drive in the eighth.
NATIONALS (SS) 6, MARLINS 3
Jeremy Hellickson made his Washington debut, allowing one run in four innings while striking out four. Starlin Castro had two hits for Miami.
ASTROS (SS) 3, NATIONALS (SS) 1
A.J. Cole, who will begin the season as Washington's fifth starter, walked five in four innings. He yielded three runs and five hits, falling to 0-3 with a 4.85 ERA this spring.
INDIANS 6, DIAMONDBACKS 1
Cleveland newcomer Yonder Alonso had two more hits, including a home run off Arizona starter Patrick Corbin. Alonso is batting .396 with seven homers and 12 RBIs this spring.
Indians starter Mike Clevinger struck out seven and walked none over 5 2/3 innings. He gave up one run and three hits. Corbin was touched up for three runs — two earned — and six hits in five-plus innings.
PADRES 9, RANGERS 7
San Diego starter Bryan Mitchell was tagged for seven runs, eight hits and three walks in four innings. Rangers slugger Joey Gallo went 3 for 3 with two home runs off Mitchell, who also served up a three-run shot to Rougned Odor.
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