Shelby Miller has decided to undergo Tommy John surgery.

Miller, who was also diagnosed with a flexor strain, had been evaluating his options, which included trying to rehab the injury through non-surgical options.

"It's the best decision I think we could make," Miller said

Miller is 2-2 with a 4.09 ERA in four starts this season. He went 3-12 with a 6.15 ERA in 2016.

Shelby Miller has been diagnosed with a flexor strain and partially torn ulnar collateral ligament.

Miller is considering his options, including Tommy John surgery and is expected to decide soon.

The non-surgical route for Miller would include a platelet-rich plasma injection or stem cell treatment.

Shelby Miller's MRI is being sent to Dr. James Andrews for a third opinion.

Miller was asked directly if the first two readings of his MRI showed a torn ulnar collateral ligament.

"They see something in there," Miller said to reporters. "They haven't given me specifics yet, exactly what it is or how we're going to handle it or what we're going to do to fix it."

The Arizona Diamondbacks have downplayed the injury thus far.

"It's part of the plan that we had talked about all along where we were going to have this group look at it and come together and get as much information as we possibly could, and pass it along to Shelby and figure out what the best game plan is," Torey Lovullo said.

Shelby Miller left the Arizona Diamondbacks' loss to the Los Angeles Dodgers on Sunday after just four innings because of right forearm tightness.

Miller threw four shutout innings before walking two batters and giving up an RBI double. He threw one more pitch, then left after a visit to the mound by the Arizona trainer.

He will have a precautionary MRI on Monday.

Torey Lovullo said he got a signal from an Arizona player that something wasn't right and made the decision to remove Miller from the game.

"These are tough things for me to address. It is really unfortunate," Lovullo said. "Shelby has been throwing the ball really well. This is a minor setback for him but, numbers aside, you just hate to have a situation like this pop up."

Buster Posey was doing well on Monday night after being struck in the helmet by a 94 mph fastball from Arizona Diamondbacks starter Taijuan Walker.

Posey will be re-evaluated, but Bruce Bochy said, "He's doing good, he's doing fine."

Posey got up on his own after being hit but exited the game. Nick Hundley entered to pinch run and stay in the game as catcher.

Giants ace Madison Bumgarner hit two home runs Sunday to set the major league record for the most Opening Day home runs by a pitcher.

The Giants' starter hit homers in both of his at-bats. Bumgarner hit a line-drive homer against Arizona's Zack Greinke to set the record.