This release from the Yankees:
RHP Mariano Rivera will undergo arthroscopic surgery on his right shoulder on Tuesday, October 7. The procedure will be performed by Dr. David Altchek at the Hospital for Special Surgery in New York.
Mo is getting a calcification taken out that had grown above his AC joint. The growth had caused some inflammation. By having the procedure done now, he is expected to be ready for spring training. Altchek is the team physician of the Mets and earlier this year did the shoulder surgery on Jorge Posada.