PHOENIX -- Before throwing a single pitch in the regular season, San Francisco's Matt Cain wound up on the disabled list.
The Giants said Tuesday that Cain has a flexor tendon strain in his right forearm, and put the 30-year-old right-hander on the DL retroactive to April 4.
Cain will return to San Francisco for further evaluation. He could miss a few weeks, manager Bruce Bochy said before Tuesday's game against the Arizona Diamondbacks.
"It's unfortunate for Matty," Bochy said. "He's worked hard to get back on the mound, and he's had a little hiccup there, but hopefully, it won't be too long. It's hard to say. Two, three weeks, we're hoping."
Cain was scratched from his scheduled start Wednesday, and the Giants said an MRI revealed Cain does not have ligament damage in his forearm.
A three-time All-Star, Cain did not pitch after July 9 last season and had surgery Aug. 12 to remove bone chips. He had a 5.40 ERA in four spring training starts, allowing 15 hits in 11⅔ innings with seven strikeouts and three walks.
San Francisco recalled right-hander Chris Heston from Triple-A Fresno, and he is slated to start Wednesday against the Diamondbacks.
Another starter, right-hander Jake Peavy, felt continued back soreness after a bullpen session Tuesday. Peavy is in line to start Sunday at San Diego if he is cleared by medical staff, and a decision could come Wednesday.
"I hope that decision is for me to get the ball in the next few days. I'm as optimistic as I can be," Peavy said.
Brandon Belt left Tuesday's loss with one out in the bottom of the fourth inning after going for a foul ball and pulling up. He suffered a strained groin and was replaced by Joaquin Arias. Belt will have an MRI on Wednesday, Bochy said. After the game, Belt said he could lift his leg and jog but felt pain going from side to side.
"Honestly, I don't think it's too bad," Belt said. "Just do what I got to do to get back out there and, hopefully, it won't be too long."
Bochy said he's never gone through such bad luck with injuries to begin a season.
"It's something that's difficult to do with three players," he said. "You have one first baseman on the DL. Hopefully Belt's fine. So we're going through a rash of them right now. Some things you can't explain."
The Associated Press contributed to this report.