ST. LOUIS -- Alex Reyes had just completed a long, arduous road back to the big leagues. Another one now lies ahead.

On Wednesday, the Cardinals announced Reyes underwent surgery to reattach a tendon in his right lat, ending the right-hander's season after one truncated start. Dr. Anthony Romeo preformed the operation in Philadelphia, where Reyes flew to receive a second opinion after sustaining a "significant" strain in his season debut on May 30.

The Cardinals do not plan to place Reyes, the club's No. 1 prospect per MLB Pipeline, on the 60-day disabled list until the need for space on the 40-man roster requires them to, and the righty will rejoin the team after he spends several days recovering with family in New Jersey. But Reyes' season is considered over, weeks after he completed an extended recovery from Tommy John Surgery.

"Recovery time for a surgery like this is six months before he's back on a mound," general manager Michael Girsch said. "We've been told by doctors they expect him to be fully recovered."

One of baseball's most-consulted lat specialists, Romeo operated on Jake Peavy when the former Cy Young Award winner sustained a complete tear from the bone in 2011. Reyes' injury is considered less severe than Peavy's, and only peripherally similar to the one Mets starter Noah Syndergaard sustained last season, which kept him out four months.

Girsch called Reyes' injury "uncommon," and stated that the lat "wasn't completely torn off, which means there was good blood flow, which means they're very optimistic for recovery."

Reyes initially had right lat discomfort after his final rehab start at Triple-A Memphis on May 24, when he struck out 13 and flirted around 100 mph with his fastball. It's been described various ways by different sources over the nearly two weeks since, from "tightness" to "soreness" to "fatigue," which was what Reyes called it.

But the Cardinals say Reyes did not disclose it in any form until his velocity dipped precipitously last week in Milwaukee, leading to an early removal from his first Major League start in 16 months. A subsequent MRI revealed a partial tear in Reyes' right lat, its tendon partially frayed from the bone below his back right shoulder.

Wednesday's MRI in Philadelphia confirmed the diagnosis, prompting immediate surgery.

"The longer you wait, the more problematic it becomes," Girsch said. "We don't know how this progressed. No one knows quite how this progressed. It's hard to speculate when along the path it became a significant issue."

Girsch said the club was unaware of any previous discomfort when it decided to give Reyes an extra day of rest between his final rehab start and his big league return. By putting five days between Reyes' starts instead of the traditional four, "we are doing what's right for Alex," Cardinals manager Mike Matheny said at the time.

The first signs that something was wrong came two innings into Reyes' start in Milwaukee, flashing from the scoreboard at Miller Park. Though he showed no outward signs of injury, Reyes' typically high-octane fastball velocity began to oscillate. His fastball bounced between 96.8 mph and 92.8 mph, per Statcast™, for much of the second and third innings. By the fourth, it dropped to 91 mph, sending Matheny and the club's training staff to the mound in concern.

"It was a couple pitches. We watch guys do that all the time on purpose," Matheny said. "It was a chance to go ask him if everything was all right."

Maintaining his health, Reyes assured his manager everything was. He then finished the inning by firing four fastballs, all above 95 mph, appearing to temporarily prove it. But Matheny lifted Reyes for a pinch-hitter the next inning in a move billed as precautionary, finishing Reyes' debut at 73 pitches.

"We are constantly reinforcing the importance of [our players] being honest with us," Matheny said. "There is nothing our medical team can do if they aren't giving us honest answers. This isn't some great revelation of how important it is. It's always being preached. If they don't give us all the information, their odds of coming back and staying healthy aren't going to be as high. It's a tough line to walk. There is that difference between injured and pain. If you're open and honest about it, we'll give you all the resources that we have to get to the bottom of it."