Shaun Marcum will undergo season-ending surgery next Monday in St. Louis to address numbness and coldness in his pitching hand.
Marcum was examined by specialist Robert Thompson at Barnes-Jewish Hospital in St. Louis.
Thoracic outlet syndrome, which is believed to be causing the numbness, is an artery obstruction or nerve pinching caused by compression between the collarbone and first rib.
Marcum may begin tossing a baseball in two months, but would not be ready to pitch again in the majors this season.
Via Adam Rubin/ESPN