Griffin has not pitched this season after experiencing elbow discomfort during spring training and had been diagnosed with flexor tendinitis. He will be the second A's starter to be out for the season due to the surgery. Last month, Jarrod Parker, who won 12 games last season, had Tommy John surgery for the second time.
"We were certainly hoping this wasn't going to be the case," A's manager Bob Melvin. "Losing two guys like that for an entire season is a difficult blow. Losing one's a blow, two's tough. You move on, but you have sympathy for the two guys that are having to go through that because they've meant so much to this team over the last couple of years."
Griffin, 26, went 14-10 with a 3.83 ERA, 1.13 WHIP and 171 strikeouts last season for Oakland, which currently leads the American League West with a 16-10 record.
Griffin is 21-11 with a 3.60 ERA in 47 starts in two seasons with the team. SI.com STAFF: MLB Power Rankings: Braves take over top spot, AL West pair rises