Beginning a few bullpen sessions ago, every time Tristan Beck would throw, his right hand would go cold. He would begin to lose feeling. Numbness would eventually set in.

The 27-year-old right-hander brought these symptoms to the Giants’ medical staff, who recommended he visit a specialist. After being scratched from his first scheduled start of the spring Monday, Beck flew back to San Francisco, where vascular specialists at Stanford diagnosed him with an aneurysm in his upper arm, the club announced Thursday.

The outlook for Beck is unclear as he weighs treatment options, which manager Bob Melvin declined to discuss, though he ruled him out for Opening Day and said he would not pitch again for some time. Of more immediate concern was for his well-being than who might backfill his place in the starting rotation.

“We just want to make sure we get it taken care of and he moves on from there,” Melvin said. “It’s obviously not ideal.”

The condition, in which a blood vessel expands or bulges and can eventually rupture, is fairly novel within the game, where tendons, ligaments and soft tissue are usually of more concern. A 40-year veteran of the sport, Melvin said he could not remember the ailment presenting in any other player.

Citing a 1999 study in the American Journal of Medicine that found aneurysms of the axillary artery had been “reported with increased frequency” in baseball players, Dr. Nirav Pandya, an orthopedic surgeon at UCSF, said that while it is “definitely not something that is common,” there is some precedent, particularly in pitchers.

“There are some case reports over the years of pitchers getting aneurysms of their axillary artery where the pec muscles compress the artery,” Pandya said, referencing the major vessel that brings oxygenated blood from the chest to the upper arm.

If treated with surgery, Pandya said, the timetable for recovery is typically about three months. In Beck’s case, he would then need to build back up to a starter’s workload, which typically takes all six weeks of spring training.