FORT MYERS, Fla. -- From the day Miguel Sano's right elbow was first examined last October, the Twins realized that Tommy John surgery might be necessary. But "you roll the dice," assistant general manager Rob Antony said, and gamble that rest and rehab might heal the ligament and salvage his season.

The Twins rolled snake eyes.

Sano, the Twins' most promising power prospect in a generation, will undergo elbow surgery and miss the 2014 season, the team decided Saturday after an MRI confirmed that a partial tear in the ulnar collateral ligament of his right elbow has not improved. Surgeons will replace the UCL later this month, and Sano, who will need about eight months to recover, will resume his career next spring.

"When I come back," Sano vowed, "I'm same player."

The Twins certainly hope so, since Sano, a 20-year-old third baseman, is generally rated the top slugging prospect in baseball. His 35 home runs between Class A and AA last season were the most by a Twins minor-leaguer in three decades, since Stan Holmes hit 37 in 1983.

He accomplished that with an elbow that, he admits now, was bothering him during the season's final month. When he informed the Twins of the elbow pain in late October, they brought him to Minneapolis for an MRI. The Twins said at the time that the injury was minor, and after consulting with Dr. James Andrews in Birmingham, decided against surgery -- a decision that Antony said he has no regrets about.

Video (01:18): Antony: No regrets on delaying Sano surgery Video (01:18): Antony: No regrets on delaying Sano surgery

"None whatsoever. [With surgery,] he would have maybe been ready at the very tail end of the regular season," Antony said. Without it? "He might not have missed any of the season. ... If we can avoid it, let's avoid it." Doctors advised waiting to see whether the pain would subside, and Sano withdrew from the Dominican Winter League after playing just two games. The rest-and-rehab strategy seemed to work, since Sano felt fine during training camp -- but the pain returned during Thursday's intrasquad game, when he charged in for a grounder and made a rushed, awkward throw to retire Kurt Suzuki.

"You start to gain some optimism, maybe this is going to work out and he won't need it," Antony said. "But when something happens and he has a setback like that, you have to deal with it."

Now a surgeon will deal with it.

The surgery will take place in the next 10 days to two weeks and will be performed by Dr. David Altchek in New York. Altchek has performed Tommy John surgeries on Kyle Gibson, Scott Baker and Joe Nathan. Sano will fly to the Dominican Republic over the next few days to visit his family before heading for surgery. After the surgery, Sano will return to Fort Myers to begin his rehabilitation.

"It's disappointing for the organization, [but] it's more disappointing for the player," Antony said. "Everybody has to deal with some adversity in their career, and this is a setback for him, but hopefully he'll get this taken care of, he'll come back healthy and strong, and he'll be in big-league camp next year at [age] 21."

The Twins tried a similar try-to-avoid-surgery approach five years ago with relief pitcher Pat Neshek, and two years ago with draft pick Alex Wimmer. In both cases, the ligament didn't respond, and surgery was ultimately necessary.

The pain is actually less severe now than it was last fall, Sano said, but the fact that it returned so quickly convinced his doctors to change course. "You could keep running him out there and he might be able to get through it," Antony said, "but it's not going to get any better and it's not going to go away."

Since Sano is not yet on the Twins' 40-man roster, missing a season won't cost the Twins a year of his career before he can become a free agent. Since he's not a pitcher, and won't have to build up the arm strength to throw breaking balls, he should need only eight months, not a full year, to recover. He even could begin taking batting practice in about four months. And the Twins have an example of how well a player can return from such an injury on their own coaching staff -- Paul Molitor, who had the procedure done (albeit on a different ligament) in 1984 and rebounded to make the All-Star team the next year.

Sano was given the news by orthopedic Dr. Diane Dahm and athletic trainer Dave Pruemer on Saturday morning, an took the news stoically. "I'm surprised," he said. "I feel better, but when I throw the ball, I'm sore."

Staff writer La Velle E. Neal contributed to this report.