Yankees Pitcher Michael Pineda has been diagnosed with an anterior labral tear in his shoulder and is set to have arthroscopic surgery on Tuesday. Pineda will be out for the season.

The Mariners traded Pineda anlong with Jose Campos to the Yankees for Jesús Montero and Héctor Noesí on January 13.Pineda was placed on the 15-day disabled list with tendinitis in his right shoulder at the end of spring training.  He has yet to pitch a regular season game for the Yankees.

According to the New York Daily News Mark Feinsand at a Press Conference with Yankees GM Brian Cashman on Wednesday, the MRI taken at the time of the trade and the MRI taken in spring training were clean and had no sign of a shoulder tear. The tear must have happened in the last rehab start.

Dr. Christopher Ahmad who will assist in the surgery  said if rehab goes well, Pineda could be ready to pitch in major league games in 12 months. Best-case scenerio is late April 2013.