The Cardinals and co-ace Chris Carpenter on Monday discussed a second shutdown and the possibility of season-ending surgery due to continued nerve-related shoulder problems that again arose following the pitcher's most recent side session. The club scrubbed Carpenter's scheduled bullpen session Monday and has no timetable for Carpenter's next session, according to a club source. Carpenter visited Dallas-based specialist Dr. Gregory Pearl last Thursday to discuss his alternatives as he confronts thoracic outlet syndrome, a rare condition that compresses nerves and blood vessels in a region between the collarbone and rib cage. Afflicted with neck pain and shoulder weakness during spring training, Carpenter continues to experience intermittent symptoms after committing to a three-month program of rest and exercise designed to strengthen his right shoulder. Initially optimistic, Carpenter has dealt with weakness after throwing batting practice to teammates in Kansas City June 22 and last Friday's session in the Busch Stadium bullpen. The club offered no explanation why it called off Carpenter's Monday session. Manager Mike Matheny remained vague when asked about the matter following Monday night's win over the Colorado Rockies. General manager John Mozeliak could not be reached for comment this morning.