The reliever was placed on the 15-day disabled list Wednesday with what was originally thought to be a strained muscle in his throwing arm.
Further examination Thursday, however, revealed a much more significant injury. Girardi said the ligament tear means Chamberlain will probably require what has become known as Tommy John surgery -- named after the first pitcher to undergo a ligament transplant operation.
Chamberlain has a 2.83 ERA in 27 games this season with a 2-0 record. He has not allowed a run in eight straight appearances.
He is in his fifth season in the majors, all of them spent with New York.