The procedure was performed Thursday by Dr. Thomas Graham at the Cleveland Clinic Hospital. A screw was inserted to repair a fracture, suffered by Gray on a comebacker from Detroit's Prince Fielder in Oakland's Game 5 AL Division Series loss Oct. 10.
The A's say Gray now has full stability in his thumb, and he is expected to be fully recovered in time for spring training.
Gray went 5-3 with a 2.67 ERA in 12 games (10 starts) this season. He pitched eight scoreless innings in a Game 2 no-decision in which he matched Tigers ace Justin Verlander in a sensational pitchers' duel.