"We're not going to have Jarrod Parker in 2014," assistant general manager David Forst said, according to the Bay Area News Group.
Parker, who had been penciled in as the starter in the A's opener March 31 against the Cleveland Indians, was examined Monday by Dr. James Andrews after experiencing forearm tightness and soreness Friday.
Andrews performed the surgery on Parker in 2009, and Parker missed the 2010 season. He'll do the second procedure to rebuild the elbow ligament on March 25.
Parker has a 10.61 ERA in three spring starts after giving up four runs on four hits, including two homers, in a start last week against the Los Angeles Dodgers. He had forearm problems at the end of last season.
He was 12-8 with a 3.97 ERA in 32 starts in 2013. His injury is the latest blow to a pitching staff already bracing for the extended absence of right-hander A.J. Griffin, who has a sore elbow and is likely out until May.
Griffin, who went 14-10 with a 3.83 ERA in 32 starts last season, has been diagnosed with a flexor muscle strain and told to rest for three weeks, after which he can begin to strengthen his arm.
"This is why we stretched out Jesse Chavez this spring," Forst said, according to the Bay Area News Group. "And this is why we didn't trade Milone in the offseason when people were saying we had too much starting pitching. The need for [pitching] depth is always there. In this case, the five starters didn't make it to Opening Day."
The Associated Press contributed to this report.