Left-hander Trevor Wilson, who was scheduled to pitch opening day in Los Angeles, will be sidelined for at least two weeks because of a broken rib.
Team physician Will Straw said that either a cyst or a tumor caused the rib to crack. He said a biopsy had been performed.
Wilson, 25, was 13-11 with the Giants in his first full season last year.
John Kruk, first baseman for the Philadelphia Phillies, suffered a mild separation of his left shoulder when he dived for a ground ball during an exhibition in Clearwater, Fla.
Glenn Ezell, 47, a coach for the Kansas City Royals, underwent heart surgery in Haines City, Fla., and the team said the five-hour operation was successful.