The Pittsburgh Pirates say top pitching prospect Jameson Taillon has undergone Tommy John surgery on his right elbow.

The procedure was performed Wednesday in New York by Dr. David Altchek. Taillon, a 22-year-old with joint Canadian-American citizenship,is expected to miss 12 to 18 months.

Taillon began feeling pain in his elbow with two weeks remaining in spring training after being assigned by the Pirates to their minor league camp. Doctors prescribed two weeks of rest, but Taillon again felt pain when he tried to throw again.

The Pirates used the second overall pick in the 2010 draft to select Taillon from The Woodlands (Tex.) High School in the Houston suburbs and gave him a $6.5 million US signing bonus, which was then a franchise record.

Taillon has gone 16-21 with a 3.72 earned-run average in 75 games over three minor league seasons. He was scheduled to begin this season at triple-A Indianapolis, where he went 1-3 with a 3.89 ERA in six starts at the end of last season.

The Pirates also said right-handed reliever Vin Mazzaro accepted his outright assignment on Wednesday. He is expected to join Indianapolis in the coming days.