Anderson, who incurred the injury while batting against Matt Cain during Saturday's 1-0 victory over the Giants, will need to go to the 15-day disabled list. Manager Walt Weiss, who learned the extent of the injury at the beginning of his team's 5-4, 10-inning loss to the Giants on Sunday, said he had not had discussions with club officials, but he thought the team would put lefty Franklin Morales back into the rotation.
Anderson (0-2, 3.60 ERA) was having the best of his three starts for three innings before suffering the injury when he hit a Cain pitch off the end of his bat.
"One of the more frustrating parts was after the game I got some more range of motion and there wasn't as much swelling, and today it puffed up and the mobility wasn't what it was the day before," Anderson said. "I knew something was probably wrong, but I didn't know what the extent of it was.
"It's really frustrating. About the time that you kind of show your new teammates why they traded for you, you're showcasing some of your ability, then something like this happens."
Anderson will be sent to Denver to see a hand specialist to determine the treatment plan and pinpoint the expected time missed, Rockies head athletic trainer Keith Dugger said.
The injury had a freak nature to it. Dugger said he had never seen such an injury to that part of the finger from a swing. Anderson said usually when someone hits a ball the way he did, the bat breaks and takes some pressure off the hand.
"I guess the wood I had was too strong," he said.
Anderson, 26, had Tommy John surgery in 2011 and last season had foot and ankle injuries while with the Athletics.
"It's a freak deal," he said. "Obviously, I've had the shadow of the injury bug around me, but there's nothing I can do about it. I swung and broke my finger."