Joe Stiglich of CSNBayArea.com, citing a source “with knowledge of the situation,” reported the new development on Friday.
Griffin was shut down with tightness in his forearm and elbow soreness after throwing 8.2 innings in Cactus League action, where he allowed 10 runs on 19 hits in 8.2 innings. He last appeared in a game on March 13.
Griffin becomes the second A’s starter to undergo Tommy John surgery this season, joining Jarrod Parker, who had his second ligament replacement procedure performed last month.
Griffin, 26, was 14-10 with a 3.83 ERA and 1.125 WHIP for the A’s in 2013, starting 32 games and working 200 innings, striking out 171 hitters and leading the American League, allowing 36 home runs.
He made one start in the AL Division Series against Detroit last October, taking a no-decision after working five innings and allowing two runs on seven hits with one strikeout in Game 4 of the series, a game the A’s eventually won 4-3 with a three-run rally in the bottom of the ninth.
Griffin was a 13th-round pick of the A’s in the 2010 amateur draft out of the University of San Diego and he made his debut with Oakland in June 2012.