BALTIMORE -- Top pitching prospect Dylan Bundy will undergo Tommy John surgery on his right elbow on Thursday, effectively ending the 20-year-old's season and sidelining him for approximately 12 months.

Bundy was re-examined in Florida by Dr. James Andrews on Wednesday after suffering a setback during his rehab earlier in the week, and he was diagnosed with a partial tear in his elbow ligament. The surgery -- which will be performed by Andrews -- typically requires a year of rehab/recovery, but it varies in each particular case and is a significant blow for an Orioles club that could have used the right-hander at the big league level this season.

"It's because of where he was drafted and what our hopes are," Orioles manager Buck Showalter said of the buzz around Bundy's season-ending surgery.

"He had some roads to cross, and this might help him some in certain situations. Hopefully, next year this time we'll be putting a date on when he is going to pitch again in a game. And we all know, obviously there are a lot of exceptions, but this is a procedure that has become, unfortunately, pretty commonplace, as Dr. Andrews would say."

The fourth overall pick in the 2011 First-Year Player Draft, Bundy -- who netted a $6.25 million signing bonus -- was ranked the No. 2 prospect in baseball by MLB.com entering the season. But he never looked quite right this spring and was optioned to Double-A Bowie early in camp, last throwing off a mound in March.

Bundy was shut down when the injury -- originally diagnosed as right flexor mass tightness -- first crept up, and he sought a second opinion from Andrews, who administered a PRP (platelet-rich plasma) injection on April 29 and prescribed six weeks of rest.

There were no previous issues in Bundy's rehab until Monday, when he felt discomfort throwing from 120 feet of flat ground at the team's spring facility. That prompted a re-evaluation by team orthopedist John Wilckens and another visit to Andrews, at which point he was diagnosed with the partial tear.

"Having given it two [separate] times rest and treating it conservatively, that was an indication that something else needs to be done to allow him to be a capable pitcher," executive vice president of baseball operations Dan Duquette said. "At 20 years old, he should be able to come back and effectively pitch."

Duquette said the organization's initial approach was to avoid surgery, and that trying more conservative options to treat the injury is always preferred given the length of the recovery road with a ligament-replacement procedure.

Showalter said he was not aware of the injury showing up on previous MRIs.

"I just know where we are and where we've got to get, and we'll get there and he'll pitch well for us," Showalter said of Bundy, who flew through the Minors last season and made his big league debut in September. "I think the key where that's concerned is now we've got that behind us. We know what it is. It's nothing he is doing wrong or something he's got to do differently. It's just something that happens. Pretty normal. And we're going to fix it.

"I think if anybody knows Dylan, he'll be very diligent with his rehab. If anything, we'll have to watch him being too diligent. That's a big part of it. If you are willing to go through the rehab … where he's concerned, whether he wants to pitch for us or not. And he does."

"Dylan is a hard worker and he's very stubborn," Duquette added. "He has some good qualities to be a good pitcher. The rehab is a challenge because you got to go through different progressions and stages, so it's important he works closely with the therapist. I'm sure Dylan is up to the task of rehab."

Bundy, selected out of Owasso (Okla.) High School, went 9-3 with a 2.08 ERA in 23 combined starts between two levels of Class A and Double-A before being promoted to the big league club in September. He appeared in relief for the Orioles during the final month of the regular season and was -- if healthy -- considered an option for the Orioles again this year.

"It's unfortunate for Dylan that he had the injury, that he's going to miss time for his career," Duquette said. "Fortunately for the Orioles, we have other pitchers. We have some pitching depth. It's just the right thing to do at this time."