SCOTTSDALE, Ariz. -- The Giants’ starting rotation took a significant hit Thursday, when the club revealed that right-hander Tristan Beck has been diagnosed with an aneurysm in his upper arm.

Beck said he will undergo surgery at Stanford on Monday to address the issue, which will rule him out for Opening Day and leave San Francisco without its projected No. 5 starter for an indefinite amount of time. Beck said he’ll have a better sense of his recovery timeline after he comes out of the surgery, but he hopes to return to the mound before the end of the season.

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Beck, 27, felt his hand go cold after throwing some bullpen sessions early in camp, prompting the Giants to send him back to San Francisco to be evaluated by team doctors. Beck ended up visiting a vascular specialist at Stanford, who helped determine that an aneurysm -- an abnormal bulge or ballooning in the wall of a blood vessel -- was the source of the numbness.

Aneurysms are fairly uncommon as far as baseball injuries go -- manager Bob Melvin couldn’t recall another situation in which one of his players dealt with one -- though former Yankees and Mets starter David Cone missed four months after undergoing surgery to remove one in his right shoulder in 1996. Cone twirled seven hitless innings in his first start after the procedure and ended up pitching in the Majors for six more seasons, two of which were All-Star campaigns for the Yankees.

“There’s probably some relief in knowing that if it’s taken care of right, that you can be as good if not better than ever,” Melvin said. “You hear that word [aneurysm], it certainly gets your attention, but I think he’s in a good place right now.”

Still, the setback was understandably disappointing for Beck, who appeared in line to be a major contributor in the rotation after logging a 3.92 ERA over 33 appearances (three starts) for the Giants in 2023.

“Disappointment is definitely the operative word,” Beck said. “Devastation. All that. But it’s interesting. This feels different. I’ve had injuries in the past, and there’s definitely two sides to this. Obviously, I came in with an opportunity to go out there and compete for a really meaningful role on this team. That meant a lot to me. … It’s disappointing to not be able to follow through on that, at least early.

“Then there’s kind of the flip side. This is something that could have been a little more serious. Something that kind of feels like it has more off-the-field implications. I’m just really thankful for the great people we have around. The fact that this was just absolutely textbook by the Giants’ medical [staff] and all parties.”

Beck’s condition will further thin a San Francisco rotation that was expected to lean heavily on young pitchers early in the year. Keaton Winn (the Giants' No. 16 prospect) also has been slowed by mild right elbow soreness this spring, though the Giants still expect the 26-year-old right-hander to have enough time to get stretched out and join Logan Webb, Kyle Harrison and Jordan Hicks in the Opening Day rotation. Who else might round out the group remains unclear.

Sean Hjelle, Mason Black (the Giants’ No. 9 prospect) and non-roster invitees Spencer Howard and Daulton Jefferies are among the internal candidates who could make a push for the final rotation spot and help cover innings while veterans Alex Cobb (left hip surgery) and Robbie Ray (Tommy John surgery) work their way back from injuries, but none has recorded a clean outing in Cactus League play thus far. Kai-Wei Teng could also jump into the mix, though he suffered a left oblique strain at the beginning of camp and is only now ramping up to throwing bullpen sessions again.

There are, of course, a few established free-agent starters who are looking like increasingly obvious fits for the Giants, including left-handers Blake Snell and Jordan Montgomery. Not that Melvin needed any reminding.

“You think?” Melvin said. “We’re always looking to try to improve the team.”

Melvin knows Snell particularly well after managing the reigning National League Cy Young Award winner in San Diego over the past two seasons. Snell, 31, recorded an MLB-best 2.25 ERA over 32 starts last year, though he also issued a league-high 99 walks over 180 innings.

Montgomery, 31, recorded a 3.20 ERA over 32 starts between the Cardinals and Rangers in 2023, helping to carry Texas to its first World Series win in franchise history.

Snell and Montgomery are both represented by Scott Boras, who recently negotiated a three-year, $80 million contract between Cody Bellinger and the Cubs that included opt-outs after the first and second years of the deal. The Giants signed another Boras client -- left-hander Carlos Rodón -- to a two-year, $44 million contract with an opt-out after the first season in 2022, so they could try to take a similar approach to Snell or Montgomery if either are open to shorter-term deals.